ASC/N2 Bus Network/Troubleshoot Guide
Contents
1. Self Termination N2 Bus ASC ASC ASC ASC Self Self Self Self Self Termination Termination Termination Termination Termination EOLS3 Figure 9 Example Three Repeater Used on N2 Bus 18 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Important N2 Bus Table 4 lists characteristics of various Companion devices that are Characteristics important to installing and commissioning these devices Note that some devices do not have EOL jumpers but have the bias voltage permanently applied to the N2 and N2 lines Other devices may or may not have isolation of the REF line to the device s ground Isolation problems with communication could possibly result depending on the situation in which the N2 lines are used Refer to the Troubleshooting N2 Bus Installation section of this document for more details Table 4 N2 Bus Characteristics for Various Companion Devices Device Isolated N2 REF Connection N2 Protection Bias EOL Type N2 Value Type Y Transformer isolated from digital Transient voltage 100K ohm Self common and earth ground suppressors and PTC on Termination unit CPN201 Y 100 ohm resistor to isolated Transient voltage 1 2Kohm Jumper transformer common suppressors and PTC on unit LCP Transformer isolated from digital Transient voltage 100Kohm Self common and earth ground suppressors 2 Termination MM CVT1013 100 ohm resistor to commo2. PHP Ch 1 2 Vidiv Tidiv 5 mS SCOPESG Figure 15 N2 Bus Signal as Measured with Oscilloscope 28 Introduction ASC and N2 Bus Networking and Troubleshooting Guide 6 Connect channel B to the N2 wire and connect channel A to the N2 wire Do not use the oscilloscope ground lead 7 Compare the signal you measure with the waveform in Figure 15 They should resemble the figure A signal outside this range indicates that the N2 Bus is not functioning properly Note At the dead time between messages you can measure the bias voltage In this figure it is 0 5 VDC Factors that can cause improper signal levels are e N2 Bus wires are not polarized correctly i e wires are reversed e N2cable runs are too long e breaks in the 24 AWG wire e an ASC has malfunctioned e N2 Bus is improperly terminated e g EOL jumpers configured improperly e N2 Bus contains too many devices loading down the bus e N2 Bus wiring has T or Y connections installed Check all wiring and devices to pinpoint the problem Replace parts if necessary Diagnostic The AHU102 0 has two diagnostic LEDs that indicate whether the LEDs on the controller is communicating over the N2 Bus and Zone Bus During AHU normal operation the two LEDs are used as Table 6 shows Table 6 Diagnostic LEDs on AHU102 0 Controller Single blink The AHU is receiving but has not transmitted over the N2 Bus during the past 1 5 seconds Double blink
3. The AHU is receiving and transmitting data over the N2 Bus Bottom LED Single blink The AHU is transmitting but not receiving over the Zone Bus Zone Bus Double blink The AHU is transmitting and receiving data over the Zone Bus Top and Double blink The AHU102 0 is resetting An Al point with a value Bottom LEDs together greater than 10 VDC is most likely causing this Together problem Check current inputs Both off Power to the AHU is not on Check the green LED on the AHU101 motherboard Introduction ASC and N2 Bus Networking and Troubleshooting Guide 29 30 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Installing UNTs Used with Gas Ignition Devices Gas ignition devices for rooftop units require that you use shielded wiring to a UNT Controller These devices generate very high levels of electrical noise that can interfere with N2 communication For information about how to install these devices in rooftop units refer to the UNT Controller Technical Bulletin in this manual Introduction ASC and N2 Bus Networking and Troubleshooting Guide 31 32 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Quiet Wiring vs Noisy Wiring Using Enclosures for ASCs Hard and Soft Grounding Metasys Installation Practices This document uses the terms quiet wiring and noisy wiring With wiring gas ignition devices especially it is important to know the difference be
4. 120 VAC source into a 120 VAC source N2 Bus polarity is incorrect Re wire N2 Bus wires for proper polarity AHU continually An Al point greater than 10 VDC is Disconnect the Al or insert the resets connected to the AHU102 current jumper ASC cycles A read only point is defined in the Delete the AO or BO point and read online and Companion data base as a itas an Al or BI point to the offline read write point AO or BO Companion data base A Companion process is using an Delete the use of the unconfigured unconfigured point i e not listed point in the Companion process in HVACPRO SYM file Two or more ASCs have the same Change each duplicate ASC address address to a unique number AO and BO The UNT111 was downloaded as Re download the UNT this time points on the a UNT110 specifying it as a UNT111 UNT 111 are not communicating UNT is offline Points BO 9 and BO 10 are Delete the use of BO 9 and BO 10 defined in the UNT data base from the data base UNT100 101 or The UNT100 101 or VAV is Disconnect the ground between the VAV is offline grounded through the Companion devices PC or through another UNT100 101 or VAV ASC does not Two or more ASCs have the same Change each duplicate ASC come online address address to a unique number The address of the ASC was Cycle power on the ASC changed without its power being cycled afterward The ten minute delay after Wait until the delay expire
5. Bus Networking and Troubleshooting Guide Example Two Figure 8 In Figure 8 the N2 Bus has a row of ASCs If the Companion PC or Panel LTD is somewhere in the middle of the N2 it would have its EOL jumpers set to the In position even though this device is not physically at the end of line This is because at least one jumpered EOL is needed per bus Companion Panel LTD Version Companion PC Version We J D Panel EOL In MM CVT101 Converter EOL In ay yy ASC ASC ASC ASC ASC Self Termination Self Termination Self Termination Self Termination Self Termination EOLS2 Figure 8 Example Two Companion PC Panel LTD Terminated Introduction ASC and N2 Bus Networking and Troubleshooting Guide 17 Example Three Figure 9 In the third example Figure 9 a repeater is placed near the middle of the N2 Bus Side A of the repeater has its EOL set to Out but side B has its EOL set to In since its segment needs a jumpered EOL Also the Companion PC or Panel LTD has its EOL jumpers set to In Companion Panel LTD Version Companion PC Version Repeater N A B A EOL Out or K E m gt ba gt MM CVT101 Converter EOL In
6. Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of entering the enclosure with a 560 pF capacitor EXAMPLE3 Figure 18 N2 Bus with Devices Divided in Two Separate Enclosures 38 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Suppression Devices In most installations reliable controller operation is ensured by a separate isolation transformer or step down transformer to provide 24 VAC toa UNT or VAV Controller However in environments where transient electrical noise is present on power lines you must take further precautions to prevent unwanted BO cycling or other possible controller malfunctions Also the switching of inductive loads can generate transients that can be conducted and or radiated into the circuits controlling those loads as well as into other circuits nearby While the practices described in a previous section Rules for Using Shielded Cable are intended to lessen the effects of such transients on field wires the transients on the power line can be significantly reduced in either of these ways e Connect an Metal Oxide Varistor MOV across the UNT supply transformer primary The MOV must be rated appropriately for the line voltage For your application refer to Table 7 and select the correct MOV e Or use a Split Bobbin transformer rather than a standard non isolated transformer to attenuate electrical noise For 120 VAC
7. line applications we recommend the AS XFR100 1 as a step down transformer Note For the N2 Bus the recommended suppression device is the Transient Eliminator model TE JC04C12 made by Advanced Protection Technologies APT For details refer to the N2 Communications Bus Technical Bulletin in the Metasys Network Technical Manual The most effective location for the suppression device is directly across the load since it lessens the propagation of transient energy into connected wiring which in turn becomes a source of noise to adjacent wiring Difficulties in getting access to the load however may sometimes make it necessary to locate the suppression device at the ASC Introduction ASC and N2 Bus Networking and Troubleshooting Guide 39 40 Table 7 Recommended Suppression Devices MOVs Power Transformer Primary Voltage fs 120 VAC 208 to 240 VAC 277 VAC 347 VAC Minimum Continuous 130 to 135 VRMS 250 to 280 VRMS 300 to 320 VRMS 385 VRMS Voltage Rating Only 250 V types listed Minimum Energy 30 Joules 55 Joules 80 Joules eee Joules Rating Minimum Peak 4 000 Amps 4 000 Amps 4 000 Amps ices 000 Amps Current 8 x 20 second pulse V130LA10A V250LA20A None None V130LA20A V250LA40A V130LA20B V250LA40B V130K14 V250K14 V300K14 V385K14 D6321Z0V131RA15 D63821ZOV251RA90 D6321Z0V301RA105 D6521Z0V131RA20 D6521Z0V251RA130 D6521Z0V301RA150 D6921ZOV131RA09 D6921ZOV251RA72 D6921Z0V301RA80 Mallory VSAC14D
8. lt 1200 ohm l Panel LTD gt REF EOLWIRE2 Figure 5 End of line Wiring for MM CVT101 and Panel L TD Companion Figure 6 shows an electrical drawing of the end of line wiring for the AHU VAV UNT and LCP controllers F 5VDC 100K ohm N2 t l MAA ASC S S Es EN P i N gt HR ou gt o 18 50K Pa c ae lt ohm N2 P Lo PRC Microprocessor lt 100K ohm REF EOLWIRE1 Figure 6 End of line Wiring for AHU VAV UNT and LCP Controllers The EOL terminations on the MM CVT101 and Panel LTD Companion place a e direct current bias on the N2 wires e 220 ohm resistor from the N2 to the N2 lines to terminate them The bias prevents the lines from floating If no communications were taking place and all the EOL jumpers were set to the Out position the N2 and N2 lines would float That is to say the bus would have no definite voltage or signal The receivers would interpret the floating N2 signal as data albeit bad data To avoid this and to provide some impedance termination one or two end of line terminations must be made on each N2 Bus segment 14 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Proper EOL Settings With the EOL jumpers set to the In position a positive bias voltage is applied across the N2 and N2 lines This bias voltage is referenced to the REF line The bias resistors and the
9. ten seconds for the reset Communication Resetting takes ten seconds aftera period to expire before trying to Error download commission the controller Bad CRC The Cyclical Redundancy Check of Check for tight and proper the message received is incorrect connections between the laptop due to an error in transmission PC Cable Pro and the ASC Invalid response The message received is not what the HVAC PRO for Windows Load utility expected Introduction ASC and N2 Bus Networking and Troubleshooting Guide 47 An effective troubleshooting technique is to use a CBLCON and watch its LEDs Refer to Table 10 The LEDs will indicate the problem Another technique is to exchange the component that is believed defective with a working component of the same type If the error no longer occurs the component is defective A noisy wire adjacent to the Zone Bus can also cause communication errors Noise can be periodically induced into the Zone Bus thereby causing sporadic communication failures between the laptop and the ASC Most often noisy lines cause intermittent disruption not total loss of communication For more information on the HVAC PRO for Windows refer to the HVAC PRO for Windows User s Manual FAN 637 5 JQHNSON CONTRELS Controls Group FAN 636 3 507 E Michigan Street Application Specific Controllers Technical Manual P O Box 423 Printed in U S A Milwaukee WI 53201 48 Introduction ASC and N2 Bus Networking and
10. the HVAC PRO for Windows commissioning tool with the ASCs over the Zone Bus Often the cause of the error is a loose or improper connection between the Cable Pro AS CBLPRO laptop PC and the controller A defective COM port on the laptop could also be at fault Other times a defective controller can cause an error Realize that it takes ten seconds for an ASC to reset and resume communication after being downloaded or after exiting HVAC PRO for Windows Table 11 Zone Terminal Communication Errors on Download Error Number Cause Description or Not Displayed Description Undefined command The device is being sent a message Check for tight and proper that contains an invalid command connections between the laptop PC Cable Pro and the ASC Invalid message size The size of the message sent does not correspond to the type of message sent Invalid command The command issued is not valid for the data type Not ready The ASC cannot process this Cycle power on the ASC If message at this time For example problem persists return ASC for the EEPROM is not functioning repair or replacement properly Bad E Write A known problem with the EEPROM Return the ASC for repair or exists replacement No communication Some hardware problem exists such Check for tight and proper as a loose connection or a failed connections between the laptop component PC Cable Pro and the ASC Hardware Controller is still in reset mode Wait
11. to 100 per second The bus interface sustains no damage in presence of fault voltages of 24 VAC M100C actuators must be powered with separate transformers therefore only the Zone Bus and Common wires need to be pulled Introduction ASC and N2 Bus Networking and Troubleshooting Guide 43 Cable Pro The AS CBLPRO is an interface device for use between a PC or laptop Description computer running HVAC PRO software and ASCs It is used for data base downloading uploading or commissioning via the Zone Bus communication port There are three models the AS CBLPRO 0 Figure 19 AS CBLPRO 1 also Figure 19 and AS CBLPRO 2 Figure 20 e When used with a Zone Bus device such as the AHU UNT VAV or ZT the Cable Pro is strictly an electrical interface between the serial RS 232 port of the computer and the Zone Bus Cable Pro operates on 24 VAC drawn from an ASC over the wire used to make the Zone Bus connections The data rate on both the RS 232 and the Zone Bus is 1200 baud e When used with the LCP Cable Pro is an asynchronous to synchronous converter as well as an electrical interface The internal microcontroller allows the RS 232 port to operate at 1200 baud while the LCP side operates at 600 baud The connection to the LCP is made with a 4 pin connector The Cable Pro needs an external 9 12 VDC VAC 60 mA power transformer for LCP service port communication e g Radio Shack 12 VDC transformer kit 273 1652 A DB9 or DB25 co
12. usually necessary for safety reasons Hard ground is also referred to as earth ground chassis ground building steel building counterpoise and green wire ground Soft Ground an electrical connection to earth ground through a capacitor such as a 560 pF capacitor A soft ground provides high frequency signals such as 10 MHz a low impedance path to earth Power line frequencies such as 50 60 Hz provide a high impedance to the earth Introduction ASC and N2 Bus Networking and Troubleshooting Guide 33 In most equipment locations whether or not to provide a low impedance connection to earth ground depends on the circumstances The high frequency components of electrical noise can render a long wire connection to ground practically useless because of the wire s inductance Wherever possible connecting a shield to a large sheet metal enclosure such as a rooftop unit is much better than trying to find a true earth ground If a metal enclosure is not available tie the shield to one of the following ground connections listed in order of preference 1 Direct bond to building counterpoise ground system 2 Direct bond to main building structural steel e g bolt into threaded hole 3 Bond to ground rod installed a minimum of two feet below minimum water table depth 4 Bond to conduit or electrical distribution box 5 Bond to nearby metal water pipe preferably copper Note In all cases make the bond to ground as sh
13. you to read the DC bias voltage Plug in the converter s transformer into a 120 VAC source If you have a Companion Panel LTD Version make sure the Panel LTD is powered with 24 VAC Note that the voltage reading on the DMM may fluctuate since the bus will be communicating Connect the DMM across the N2 and REF screws on the N2 terminal block Figure 14 Write down the DC voltage reading Repeat for N2 and REF then for N2 and N2 Compare the voltages you read on the DMM to the following values N2 to REF 2 45 to 2 98 VDC N2 to REF 2 06 to 2 54 VDC N2 to N2 0 36 to 0 92 VDC If your readings are not approximately within the ranges listed above that particular wire is grounded shorted or crossed with another wire Correct and measure again If your readings are approximately within the ranges listed above the bus is properly wired N2 Bus Terminal Block on N2 Bus Terminal Block MM CVT101 or Panel LTD Companion UNT VAV AHU LCP N2 E oO NS Pf a N2 N2 N2 N2 C N2 ve G 2 IPSE O REF REF lan i UO GND DMM f A RALAS J zBus ce es N2 to REF N2 to REF N2 to N2 2 45 to 2 98 VDC 2 06 to 2 54 VDC 0 36 to 0 92 VDC Note For best reading place probe on metal plate inside terminal not on screw POLARTY Figure 14 Test for N2 Bus Shorts Crossed Wires Grounds Introduction ASC and N2 Bus Networking and Trou
14. 2 Bus wiring Step 4 Follow the steps specific to your installation 1 If you have a Companion PC Version remove the 25 pin RS 232 connection from the MM CVT101 converter This removes the fluctuating voltage due to communications and allows you to read the DC bias voltage Disconnect the N2 Bus wires Wire the transformer to the MM CVT101 and plug into a 120 VAC source If you have a Companion Panel LTD Version disconnect the N2 Bus wires from the Panel LTD Wire 24 VAC to the Panel LTD 2 Connect the DMM without a 100K ohm resistor installed across the N2 and REF inputs on the N2 terminal block Figure 10 Write down the DC voltage reading Repeat for N2 and REF then for N2 and N2 Compare the voltages you read on the DMM to the following values N2 to REF 2 45 to 2 98 VDC N2 to REF 2 06 to 2 54 VDC N2 to N2 0 36 to 0 92 VDC If your readings are not approximately within the ranges listed above the N2 EOL device jumpers are probably set incorrectly For the PC Version ensure that pins 1 and 2 on both W1 and W2 of the MM CVT101 are jumpered EOL In For the Panel LTD Version pins 1 and 2 on both W2 and W4 of the Panel LTD circuit board must be jumpered EOL In If not jumper them and repeat the DMM readings If the voltages read are still not close to those above and after connecting the ASCs to the N2 Bus the ASCs are still not communicating replace the MM CVT101 or Companion Panel LTD If your readi
15. 220 ohm termination resistors combine to form a voltage divider By taking the tolerances on the resistors and the power supply variations into account you should expect to see the following voltage levels on the N2 lines MM CVT101 is disconnected from the PC but still connected to the N2 Bus Voltage from N2 to N2 0 36 to 0 92 VDC DMM probe on N2 terminal DMM probe on N2 terminal Voltage from N2 to REF 2 45 to 2 98 VDC DMM probe on N2 terminal DMM probe on REF terminal Voltage from N2 to REF 2 06 to 2 54 VDC DMM probe on N2 terminal DMM probe on REF terminal If the difference from N2 to N2 is greater than 0 36 V your system should be able to communicate If communication is taking place voltage on the N2 Bus fluctuates and therefore the DMM will read these fluctuating voltages An oscilloscope provides a more accurate reading Setting the EOL terminations correctly on the devices connected to the N2 Bus is crucial to proper and reliable communication Follow these rules 1 Always set the EOL jumpers to In for the Companion PC or Panel LTD This device is always set as end of line because all the controllers on the N2 namely the ASCs are self terminating they do not have EOL jumpers Note that as in Figure 8 the Companion PC or Panel LTD does not necessarily have to be at the end of line 2 If possible terminate the two devices that are at the far ends of the N2 Bus If one of thes
16. 9 41 43 43 44 46 47 Overview Who Should Read This Introduction This document contains important information on how to install and troubleshoot Application Specific Controllers ASCs and the N2 Bus on a Companion PC Panel or LTD system As our experience with this system matures we have discovered certain new installation and troubleshooting techniques which are described in this document Please use this in addition to the ASC and N2 Bus technical bulletins when installing commissioning and troubleshooting ASCs or the N2 Bus In particular this document contains the following sections e Installing ASC Controllers e Installing the N2 Bus e Troubleshooting N2 Bus Installation e Installing UNTs Used with Gas Ignition Devices e Metasys Installation Practices e Zone Bus Communications If you are new to installing commissioning and troubleshooting Metasys products it is best to read and use this document in its entirety However if you are experienced with Metasys you probably can just skim this document Note To provide the greatest assurance that the ASCs will communicate after initial installation perform the earth ground test Figure 4 and the N2 Bus polarity test Figures 10 and 11 Introduction ASC and N2 Bus Networking and Troubleshooting Guide 3 4 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Installing ASC Controllers This section explains how to inst
17. Application Specific Controllers Technical Manual 636 3 Introduction Section METASYS Technical Bulletin 0995 Issue Date ASC and N2 Bus Networking and Troubleshooting Guide Introduction Page 3 e Overview 3 e Who Should Read This 3 Installing ASC Controllers 5 e Tools Required 5 e ASC Installation Steps 6 Installing the N2 Bus 11 e Background Information 11 e N2 Bus Installation Steps 20 Troubleshooting N2 Bus Installation 23 e Overview 23 e Troubleshooting Chart 24 e TEST 1 Earth Grounded 24 VAC Load 25 e TEST 2 Ground Loop Isolation 26 e TEST 3 N2 Bus Polarity Shorts Crossed Wires Grounds 27 e TEST 4 Oscilloscope 28 e Diagnostic LEDs on the AHU 29 Installing UNTs Used with Gas Ignition Devices 31 Indicates those sections where changes have occurred since the last printing 1995 Johnson Controls Inc 1 Code No LIT 6363003 2 Metasys Installation Practices Page e Quiet Wiring vs Noisy Wiring e Using Enclosures for ASCs e Hard and Soft Grounding e Using Shielded Cable in Noisy Environments e Sample Installations with Shielded Cable e Suppression Devices e Summary of Installation Practices Zone Bus Communications e Zone Bus Description e Cable Pro Description e Cable Connector Description e Troubleshooting Indicates those sections where changes have occurred since the last printing Introduction ASC and N2 Bus Networking and Troubleshooting Guide 33 33 33 33 34 36 3
18. K201U VSAC14DK391U VSAC14DK471U VSAC14DK621U her e E vaca TNR15G211KM TNR15G391KM TNR15G471K TNR23G201KM TNR23G391JM TNR23G471K TNR23G21 1KM TNR23G391KM Oneida CKE OZ130LA10A OZ250LA20A 0Z21L471 None OZ130LA20A OZ250LA40A OZ130LA20B OZ250LA40B 02211221 0216NR14 3 0216NR20 4 Panasonic ERZ C14DK201U ERZ C14DK391U ERZ C14DK471U ERZ C14DK621U e eons a E a Philips 202250551916 202250552516 292250550016 202250553816 S14K130 S14K250 S14K300 S14K385 0216NR14 3 0390NR14 3 0620NR14 3 0620NR14 3 0216NR20 4 0390NR20 4 0620NR20 4 0620NR20 4 0216NR20DB 0416NR14 3 0416NR20 4 Thomson VE17M00131K VE17M00251K VE17M00301K None E e a a E Indicates the preferred model if several are listed Introduction ASC and N2 Bus Networking and Troubleshooting Guide Summary of Installation Practices Follow these installation practices listed in order of importance 1 2 Use a line filter with gas ignition systems Use unshielded cable for your N2 Bus application The only case you need shielded cable is if the bus is routed near noisy wire which is typically from switched line voltage loads gas ignition and line voltage distribution Properly place equipment and route wiring to separate quiet wiring from noisy wiring Also use proper terminal and wire sizes to establish tight reliable electrical connections Use suppression devices on inductive or noisy loads Establish a low impedance conne
19. N2 to REF 2 45 to 2 98 VDC gt N2 N2 N2 to REF E E 2 06 to 2 54 VDC FREF _ REF a pee N2 to N2 a fe ZBus OWM owm 4 036 to 0 92 VDC We Nich Note For best reading place probe on metal plate inside terminal not on screw VOLTAGE2 Figure 11 Measuring N2 Voltages at ASC 4 Before connecting the three N2 Bus wires identify the correct voltage and polarity of each wire with the DMM The voltages should match the following N2 to REF 2 45 to 2 98 VDC referenced to REF N2 to REF 2 06 to 2 54 VDC referenced to REF REF lt 1 0 VDC VAC referenced to earth ground with 100K ohm resistor If the voltages are not within the above ranges end of line termination may not be set correctly Locate and fix the problem 5 Connect the N2 Bus wires to the ASC and continue to the next ASC Perform Steps 3 and 4 until you have connected each ASC to the N2 Bus These five steps comprise the simplest but most thorough N2 Bus test 22 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Overview Tools Required Troubleshooting N2 Bus Installation You need to troubleshoot the N2 Bus if the Companion system is not properly communicating with the ASCs This section first presents a troubleshooting table The table covers many ASC or N2 communication problems and suggests which actions to take Second specific troubleshooting tests are given Before trying one of these
20. S CBLPRO 2 2Flashes Sec Off Connected to the Zone Bus Normal Communication off 2 Flashes Sec_ Connected to the LCP Normal Communication 1 Flash Sec Connected to the Zone Bus No RS 232 Communication or 24 VAC Shorted to Zone Bus 5 Flashes Sec 5 Flashes Sec 24 VAC High Side Shorted to Earth Ground Note Remove ground fault and cycle CBLPRO power to eliminate this fault condition en co Controller Common Shorted to Zone Bus LCP Common Shorted to LCP Data Terminal Interrupted Communication No Power or No Connection to Active Zone Bus No Power or Communication for LCP Cable The AS CBLCON O0 Cable Connector Figure 21 is a cable connecting Connector device that accepts the different sizes of telephone cable connectors used Description with the ASC products so that they are able to communicate It also monitors Zone Bus communications to the ASC or ZT by red and green LEDs described in Table 10 It has a terminal strip and a ZT download switch To Metastat To UNTVAV Zone Bus Green LED 24 VAC Red LED e cs To Zone Terminal CBLCON 1 Figure 21 AS CBLCON 0 46 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Table 10 CBLCON LEDs o Jor T Nopowerto ASO SSCSC fon OFF Zone Buswie open CS Zone Bus wire shorted to Common or CBLCON 0 switch in download ats Troubleshooting Table 11 lists and describes the errors that may occur while using
21. Troubleshooting Guide
22. US COM AOCOM BOCOM Note GRDLOOP Figure 4 Testing for Ground Loops If you read 5 VDC VAC or greater the circuit is improperly isolated Follow these steps Remove all the field wires and N2 Bus wires from the ASC but leave the transformer wires attached With the DMM still connected reconnect each set of field wires one at a time until you read 5 VDC VAC or greater At this point you have discovered one cause of the ground loop Correct the problem Continue to reconnect each set of field wires until all ground loops are found and corrected You ll know that all grounds are corrected when you read less than 5 VDC VAC on the DMM However if you check all the field wires and you still read greater than 5 VDC VAC the transformer secondary is earth grounded In this case wire a 24 VAC to 24 VAC isolation transformer to the ASC and measure again If the value is still 5 VDC VAC or greater replace the ASC Binary outputs are often the culprits of ground loops Therefore we recommend that you test the binary outputs of the ASC before testing other points Remember a single earth ground is allowed on the common terminal of the LCP AHU and UNT110 111 Controllers not on the 24 VAC terminal If you read a value less than 5 VDC VAC the circuit is properly isolated A value of less than 0 10 VDC VAC indicates a completely isolated circuit Introduction ASC and N2 Bus Networking and Troubleshooting Guide 6 Connect t
23. VDC VAC the N2 Bus is properly isolated A value less than 0 10 VDC VAC indicates a completely isolated circuit Companion Panel LTD or MM CVT101 UNT100 101 or any VAV N2 A N2 N2 e REF e PER If DMM lt 1 VDC VAC OK Isolated lf DMM gt 1 VDC VAC Ground Loop RS 232 cable disconnected Note For best reading place probe on metal om plate inside terminal not on screw ane i AAA IRR KOHMRST 100K ohm 1 4 watt Figure 12 Measuring N2 Bus Wires to Earth Ground Introduction ASC and N2 Bus Networking and Troubleshooting Guide 25 b Repeat Step 3a for the other two N2 Bus wires c Atthe ASC that you suspect is causing the ground loop measure its 15 VDC or 30 VDC terminal to earth ground using the DMM in parallel with a 100K ohm resistor If the value is greater than 5 VDC VAC disconnect the N2 Bus at the ASC Measure the VDC terminal again If the value is still greater than 5 VDC VAC a ground loop is present at that ASC Locate and correct the isolation problem and measure again If the value is less than 5 VDC VAC the ground is corrected Reconnect the N2 Bus and measure again If the value is greater than 5 VDC VAC ground sources are present at other ASCs or the N2 Bus If the value is less than 5 VDC VAC the N2 Bus and ASC are properly isolated TEST 2 For this test you ll need a red LED test light a 470 ohm resistor and a Ground Loop 9 volt battery Follow these steps referring to F
24. all ASCs The VAV and UNT100 101 inputs outputs and N2 Bus connections require complete isolation from earth ground ORE Do not earth ground the 24 VAC high side of the ASC s transformer or any of the ASC s BO terminals If you do you will damage all of the interface components that are connected including the Cable Pro laptop PC Companion PC and MM CVTI1O1 In some cases earth grounding the common side of the AHUs LCPs or UNT110 111s is allowed because only one earth ground can exist per ASC Use these procedures to ensure proper isolation Test the e field device wiring for proper isolation e transformer for isolation and correct polarity termination e connected field devices transformer and ASC for proper isolation e transformer and ASC for proper VA load requirements Tools Required Obtain the following tools to perform the installation e Digital Multimeter DMM e 100K ohm resistor 1 4 watt e Double banana plug optional shown in Figure 1 available from local electronics store or ITT Pomona Stock No 34F856 or 34F845 100K ohm 1 4 watt Use double banana plug for all tests that require bp a 100K ohm resistor placed in parallel with DMM A Steps 1 Connect 100K ohm resistor under plug s prongs N 2 Insert banana plug into DMM 7 U pen 3 Connect leads of DMM into banana plug C a E A Y Y ee oe BANANA Figure 1 Double Banana Plug Used with 100K Ohm Resistor In
25. bleshooting Guide 27 TEST 4 Oscilloscope Check the voltage and polarity of the N2 DC bias voltages at the ASC Do so by connecting the DMM across N2 and REF Figure 14 Write down the reading Repeat for N2 and REF then for N2 and N2 Compare the voltages you read to the following values N2 to REF 2 45 to 2 98 VDC N2 to REF 2 06 to 2 54 VDC N2 to N2 0 36 to 0 92 VDC If your readings are not approximately at these values that particular wire is grounded shorted or crossed with another wire Correct and measure again If your readings are within these values the bus is properly wired You can use an oscilloscope to pinpoint communication faults over the N2 Bus The procedure requires a 2 channel scope with an A minus B function or an A plus B with B inverted function Follow these steps l 2 Plug the scope into a grounded electrical outlet Set both channels to 2 volts per division Both channels must have the same gain or volts per division setting With no signal applied adjust each channel s vertical position at the same graticule on the screen i e center screen Select the channel A minus B function If your scope does not have this function select the Add function channel A ADDED to B then INVERT channel B Select the 0 5 mS horizontal range AAMA EAM W fw CA tits per ad a 144 3010 V pp EEFE ee E med tar iT 1 including 0 5 VDC bias
26. ction to earth If possible install the ASCs in metal enclosures Earth ground the metal enclosures Introduction ASC and N2 Bus Networking and Troubleshooting Guide 41 42 ntroduction ASC and N2 Bus Networking and Troubleshooting Guide Zone Bus Description Zone Bus Communications The Zone Bus is a 2 wire communications bus that allows a computer to communicate with the ASC to download the ASC s data base and to communicate with Zone Terminals and M100s A third wire is used for 24 VAC power to the Cable Pro Zone Terminal and CBLCON The Zone Bus has the following specifications Table 8 Zone Bus Specifications Multidrop serial communications bus 1200 baud bits per second Recommended Cable Type 18 AWG with shield Belden 8760 or 24 AWG with no shield unshielded telephone cable Maximum Bus Length 500 feet 150 meters with 18 AWG cable or 50 feet 15 meters with 24 AWG cable Maximum Number of Devices 24 Range of Addresses 0 to 63 Voltages Logic High Voltage 4 VDC minimum approx Logic Low Voltage 1 VDC maximum approx Data Transmission 1 Start Bit low level 8 Data Bits least significant bit first 1 Stop Bit high level Each slave device e g M100C monitors the bus and responds only to messages to its address The bus data maintains integrity in the presence of transient pulses up to 40 volts peak positive or negative having a duration of up to 10 microseconds and repetition rates up
27. d the unit back for repair or replacement Most N2 devices have isolated N2 communications power supplies and therefore there is no direct path to earth ground through any of the N2 lines However there are three exceptions in which an unwanted earth ground may be introduced into the system From the MM CVT101 which is not isolated It is grounded through pin 7 of the RS 232 connector Earth ground often comes in from the ground pin on the PC s power cord or via a printer connected to the computer which in turn connects to the MM CVT101 The Companion PC itself is grounded From a surge protection module i e APT Transient Eliminator on the N2 Bus It produces a small amount of leakage to earth ground From the Cable Pro CBLPRO O or 1 only If the laptop PC is earth grounded the Cable Pro would be grounded through the RS 232 ground pin A single ground will not cause communication problems unless another earth ground path exists in the system to complete a ground loop 12 Introduction ASC and N2 Bus Networking and Troubleshooting Guide N2 Bus Rules N2 EOL Termination The ASCs have electrical protection built into the N2 Bus transceiver circuit It prevents the N2 Bus circuitry from being damaged if someone inadvertently connects a voltage source greater than 5 VDC VAC between any two or the three N2 Bus terminals Refer to Table 2 Table 2 Voltage Protection on ASCs Controller Voltage N2 Bus Circuitry Can Withsta
28. e devices is self terminating terminate the other which will have an end of line jumper In many cases this will be the MM CVT101 Companion Panel LTD or repeater 3 If only one device on the bus can be terminated jumper it as an end of line device During commissioning visually check the N2 EOL jumpers at the Companion PC or Panel LTD e For the Panel LTD version the end of line jumpers are located on the Panel s circuit board W2 and W4 e For the PC version the jumpers are located on the MM CVT101 W1 and W2 e For the repeater the jumpers are found under the top cover Introduction ASC and N2 Bus Networking and Troubleshooting Guide 15 To illustrate different possible EOL terminations consider the following examples in Figures 7 through 9 Example One Figure 7 In this example the N2 Bus begins at the PC Panel LTD Companion and connects several ASCs This is the simplest network and requires only that the PC Panel L7D is set as the end of line device Companion Panel LTD Version Companion PC Version or a N wy pc WSs S MM CVT101 Panel EOL In Converter EOL In A ASC ASC Self Termination Self Termination Self Terminatio a a as EOLS1 Figure 7 Example One Companion PC Panel LTD Terminated 16 Introduction ASC and N2
29. he DMM across the 24 VAC and the 24 VAC Common terminal of the ASC Read the voltage with all typical loads energized A reading of 24 26 VAC is required when the line voltage is nominal If you read a value less than 22 VAC make sure the primary voltage matches the transformer s voltage rating For details refer to the appropriate ASC technical bulletin and recalculate the VA requirements for the ASC You have now completed ASC installation If this ASC is to operate in standalone mode you are done with this document If the ASC is to be connected to the N2 Bus for communication to other devices go to the next section Installing the N2 Bus Introduction ASC and N2 Bus Networking and Troubleshooting Guide 9 10 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Background Information N2 Reference Lines Installing the N2 Bus The N2 Bus is a daisy chain communications line Essentially it consists of three wires which carry three signals N2 N2 and REF The N2 and N2 lines carry the actual data signals The REF line provides a common reference so that each connected device is capable of electrically receiving and transmitting data by creating a common voltage reference among all the devices connected together by the N2 Bus Three lines are required It is important that the N2 and N2 lines are twisted together which allows most induced noise common mode noise from external sources t
30. he circuit is properly isolated Usually a value less than 0 10 VDC VAC indicates a completely isolated circuit Line DAIR Voltage lt gt 24 VAC n AN A Er Pa ie 100Kohm gt 100K ohm gt 1 4 watt K 1 4 watt lt K F 4 ZYN IN TRANSFM1 Figure 3 Testing the Transformer b Determine the polarity of the transformer s leads by using a DMM referenced to earth ground without the 100K ohm resistor Connect the transformer s secondary lead with the higher voltage potential to the 24 VAC terminal on the ASC Connect the transformer s secondary lead with the lower potential to the 24 VAC Common terminal on the ASC If the field wires are not yet connected because you skipped Step 2 disconnect one 24 VAC wire or turn off AC power and terminate the field wires Reconnect power Introduction ASC and N2 Bus Networking and Troubleshooting Guide 7 8 5 Connect the leads of the DMM in parallel with the 100K ohm resistor from the DC power supply 15 or 30 VDC output terminal of the ASC to earth ground Figure 4 This tests whether the field devices the ASC and the transformer assembly are properly isolated VAV UNT100 24 VAC MIKS lt I gt 15 VDC yi 30 VDC on AHU Line Z N 24VAC Voltage 24 VAC COM Field Wiring 100Kohm lt DMM lt 5 VDC VAC OK Isolated 1 4 watt lt DMM gt 5 VDC NVAC Earth Grounded gt AICOM BICOM ZB
31. how to use shielded cable Installations between ASCs that are in separate enclosures with Shielded Cable Enclosure MM CVT101 x or Pane LTD Companion N2 Bus N2 Bus Ground within 1 inch of enclosure s EXIT Ground within 1 inch of enclosure s ENTRY Ground within 1 inch of enclosure s ENTRY HG EXAMPLE1 Notes Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of entering enclosure with a 560 pF capacitor Figure 16 N2 Bus with ASCs in Separate Enclosures 36 Introduction ASC and N2 Bus Networking and Troubleshooting Guide The configuration shown in Figure 17 indicates how to use shielded cable between ASCs and devices that are in the same or separate enclosures Metal Enclosure Companion PC or Panel LTD M100C Metal Case Notes Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of entering enclosure with a 560 pF capacitor EXAMPLE2 Figure 17 N2 Bus with Some Devices in Same Enclosure Other Devices in Separate Enclosure Introduction ASC and N2 Bus Networking and Troubleshooting Guide 37 The configuration shown in Figure 18 indicates how to use shielded cable between ASCs and devices that are in two separate enclosures Metal Enclosure Companion PC or Panel LTD Metal Enclosure Tape back shield Notes
32. igure 13 Isolation 1 Disconnect the N2 Bus wires from the Companion PC or Panel LTD 2 Assemble the test circuit as shown in Figure 13 or purchase one with a power supply of 9 volts or greater Connect the ground lead of the battery to earth ground 4 Connect the positive lead from the test light to one of the N2 Bus wires If the LED lights when you connect the N2 Bus wire that particular wire is grounded or improperly isolated Subdivide the N2 Bus in half and repeat Steps 3 and 4 Continue to subdivide the bus until you find the location of the problem Correct the grounded condition and measure again If the LED does not light when you connect the N2 Bus wire the bus is properly isolated from earth ground 5 Repeat Step 4 for the other two N2 Bus wires N2 e N2 o REF Test Circuit A a ov K VVN Red LED 470 ohm l 15 20 mA 1 4 watt yee LEDTEST Figure 13 Ground Loop Test 26 Introduction ASC and N2 Bus Networking and Troubleshooting Guide TEST 3 N2 Bus Yov ll need a DMM to perform this test By connecting the DMM to each Polarity Shorts N2 Bus wire you ll be able to detect polarity shorts crossed wires and Crossed Wires grounds Grounds Follow these steps referring to Figure 14 1 If you have a Companion PC Version remove the 25 pin RS 232 connection from the MM CVT101 converter This removes the fluctuating voltage due to communications and allows
33. n Transient voltage 1 2K ohm Jumper suppressors and PTC on unit N2 Repeater Transformer isolated from digital Transient voltage 1 2K ohm Jumper common and earth ground suppressors UNT100 1014 Tied to digital common Transient voltage 100K ohm Self suppressors and PTC on Termination unit UNT110 111 Transformer isolated from digital Transient voltage 100K ohm Self 120 1215 common and earth ground suppressors and PTC on Termination unit VAV100 1014 Tied to digital common Transient voltage 100K ohm Self suppressors and PTC on Termination unit Notes PTC positive temperature coefficient thermistor i e a temperature sensitive resistor that acts like a resettable fuse LCPs manufactured before 1 91 should not be used at the end of line LCPs manufactured after 2 92 have transient voltage suppressors for N2 and N2 protection MM CVT101 REF terminal connects to communications ground and earth ground through the PC The UNT100 101 and VAV100 101 have N2 REF connected to digital common Digital common or 24 VAC must never be connected to earth ground The UNT110 111 120 121 have isolated N2 REF Introduction ASC and N2 Bus Networking and Troubleshooting Guide 19 N2 Bus This procedure allows you to test for proper voltage and polarity of the Installation following components Steps e RS232 to N2 Bus converter MM CVT101 Steps 1 and 2 e Companion Panel LTD s RS 485 N2 Bus converter Steps and 2 e ASC N2 Bus Step 3 e N
34. nd PAH Cd SOVDCNAG SOSS O LCP lt 6 VDC VAC before 3 1 92 lt 12 VDC VAC after 3 1 92 MM CVT101 0 lt 30 VDC VAC The following table summarizes the rules and maximums allowed for installing the N2 Bus You may wish to photocopy this table and keep it handy Table 3 N2 Bus Rules Rules Maximums Allowed Only one PC Panel LTD Version Companion per N2 Bus Only daisy chained devices Maximum Number of Devices 100 devices per PC Panel LTD Version Companion 50 devices per repeater 2 repeaters cascaded Line Length and Type 5000 feet between repeaters 15 000 feet from PC or Panel LTD to farthest ASC 3 segments of 5000 feet each 26 AWG twisted pair minimum stranded 22 AWG or heavier recommended Terminations 2 switched EOL per segment preferred 1 switched EOL per segment required The N2 Bus uses End of Line EOL terminations through the use of jumpers on the Companion Panel LTD RS232 to N2 Bus converter MM CVT101 and repeater N2 Bus circuitry in the ASCs is self terminating Figure 5 shows an electrical drawing of the end of line wiring for the MM CVT10 1 and the Panel LTD Companion Introduction ASC and N2 Bus Networking and Troubleshooting Guide 13 td Ga E OAT gy wee Beye SA OS 2 END ey a A 5vDC 1200 ohm N24 O i o I TN i Nan E WP ae S IN gt R Hout gt FOL T VT lef l An Switch ohm N2 ae 1 W2 MM CVT101 PRC Microprocessor W4 Companion
35. ngs are approximately within the ranges listed above the N2 EOL device jumpers are set correctly Go on to Step 3 20 Introduction ASC and N2 Bus Networking and Troubleshooting Guide N2 Bus Terminal Block on MM CVT101 or Panel LTD Companion C N2 Loe N2 to REF 2 45 to 2 98 VDC C Ne anne N2 to REF phere 2 06 to 2 54 VDC AN GND N2 to N2 0 36 to 0 92 VDC DMM Note For best reading place probe on metal plate inside terminal not on screw VOLTAGE Figure 10 Measuring RS 485 N2 Bus Converter Circuitry Power the ASC For LCPs manufactured before January 1991 go on to Step 4 For LCPs manufactured after January 1991 and all other ASCs continue with this step Before connecting the N2 Bus check the voltage and polarity of the N2 DC bias voltages on the ASCs Do so by connecting the DMM across N2 and REF Figure 11 Write down the reading Repeat for N2 and REF then for N2 and N2 Compare the voltages you read to the following values N2 to REF 2 45 to 2 98 VDC N2 to REF 2 06 to 2 54 VDC N2 to N2 0 36 to 0 92 VDC If your readings are not approximately at these values and the ASC does not communicate replace the ASC If your readings are within these values go on to Step 4 Introduction ASC and N2 Bus Networking and Troubleshooting Guide 21 N2 Bus Terminal Block UNT VAV AHU LCP N2 gt Ne as SA
36. nnector is used to connect the Cable Pro to the computer s RS 232 COM port The connector is supplied with the AS CBLPRO O and 1 models and permanently attached to the AS CBLPRO 2 model After connecting it make sure the Cable Pro is about a foot or more away from the computer monitor and system unit In some cases a computer monitor and system unit will give off electromagnetic noise that may disturb Cable Pro communications Therefore do not position the Cable Pro near the monitor or system unit s To Power To LCP 12VDC To ASC Zone Terminal Metastat CBLPRO 0 Figure 19 Cable Pro Model AS CBLPRO O 1 44 Introduction ASC and N2 Bus Networking and Troubleshooting Guide AS CBLPRO 2 Zone Terminal n Gann Metastat SS A To Laptop PC CBLPRO 2 Figure 20 Cable Pro Model AS CBLPRO 2 The AS CBLPRO 2 Figure 20 is an improved model of the original Cable Pro AS CBLPRO O 1 It has the following improvements e The laptop PC cable is permanently attached to the Cable Pro making PC attachment more convenient e The unit has protection against earth ground faults that may be introduced into the system e Two diagnostic LEDs indicate the status of communication of the Zone Bus and the LCP RS 232 connection Descriptions of these LEDs are printed on the unit and summarized in Table 9 Introduction ASC and N2 Bus Networking and Troubleshooting Guide 45 Table 9 Descriptions of Diagnostic LEDs on A
37. nted Earth Grounds Where circuit reference is provided by a third conductor the connection between circuit common and the third conductor must contain some resistance e g 100 ohms to limit circulating currents when other ground connections are provided for safety For the Companion system the 100 ohm resistor is located in the RS232 to N2 Bus converter MM CVT101 0 or in the Companion Panel LTD With N2 Bus grounding in mind there are a few important facts to know If earth grounded the UNT 100 101 units and all VAVs may experience communication problems This is because the REF line in these units is connected internally to digital common The UNT 100 101s and all VAV controllers are not designed to be earth grounded although they often become grounded because field wires connect to earth grounded field devices and thus bring ground into the digital common of the device During installation and commissioning ensure that no UNT 100 101s or VAVs are earth grounded This does not apply to the newer models that isolate the N2 from digital common including UNT110 111 120 121 all AHU and all LCP models According to RS 485 specifications the REF protection on most devices is a 100 ohm resistor If you miswire the MM CVT101 or Companion Panel LTD by connecting any voltage greater than 5 VAC you may damage the 100 ohm resistor The resistor is not field serviceable so if the REF line becomes damaged you ll need to sen
38. o affect both lines equally thereby canceling the noise In most installations the N2 Bus works fine with unshielded cable However in noisy environments such as near gas ignition devices and arc welders shielded twisted wire must be used Otherwise the noise disrupts N2 communications and the ASCs For more details refer to the section Metasys Installation Practices An important feature of the N2 Bus is opto isolation Isolation prevents interruption of all N2 Bus communication if any of the controllers on the bus become grounded Table 1 below outlines which controllers have opto isolation in their N2 Bus circuitry Table 1 Opto lsolated Devices re Yes The Reference REF line helps to provide a common reference from which each device connected to the N2 Bus can discern the voltage levels and hence the data on the N2 and N2 lines The N2 Bus may connect devices that are far apart such as in two different buildings by allowing line lengths of up to 15 000 feet with two repeaters If the N2 Bus is wired between buildings a surge protection module should be used at both ends Realize that connecting the earth ground of one building to the earth ground in another building can cause current to flow in the line that connects the two grounds together Because of this the EIA Standard RS 485 the N2 Bus specification states Introduction ASC and N2 Bus Networking and Troubleshooting Guide 11 N2 Bus Grounding Avoiding Unwa
39. on relay Repeat the DMM test If the LED does not turn On or you read a value greater than 1 Megohm the circuit may be properly isolated It will not be isolated if there are earth grounds that exist at higher voltages A value of infinite ohms indicates a completely isolated circuit at approximately zero volts Connect this wire to the appropriate ASC terminal and check the next wire Field Device IN OUT IN OUT COM m or LED Test Circuit Preferred Method B 0 0 E AAA mea Red LED 470 ohm 15 20 mA 1 4 watt ISOCIRCT Figure 2 Testing for an Isolated Circuit 6 Introduction ASC and N2 Bus Networking and Troubleshooting Guide 3 a Before connecting the transformer to the ASC connect the input power to the primary leads of the 24 VAC transformer Measure the voltage of each secondary transformer lead to earth ground with the DMM in parallel with a 100K ohm 1 4 watt resistor Figure 3 if using double banana plug insert plug into DMM If you read 5 VDC VAC or greater the transformer is earth grounded If this isa VAV or UNT100 101 you ll need an isolation transformer in order to isolate the connections from earth ground and protect system components Wire a separate 24 VAC to 24 VAC isolation transformer such as the Y65 to the ASC If this is any other ASC make sure the ground is on the common side of the transformer not on the 24 VAC side If you read less than 5 VDC VAC t
40. ort as possible Derate a ground point by one level in order of preference for each 50 feet of conductor run between the ground point and the equipment to be grounded For example a water pipe bond located 10 feet away is preferable to a structural steel bond located 150 feet away The recommended gauge for the ground wire is 10 or 12 AWG Using Shielded Metasys was specifically designed to use unshielded cable In most Cable in Noisy situations the N2 Bus functions reliably with this type of cable Environments However some devices emit very high levels of electrical noise Examples include radar magnetic resonance imaging equipment arc welders and gas ignition systems Use shielded cable for these devices A gas ignition system requires that you use shielded cable on the sections of the N2 Bus that are close to the spark This section outlines the standard practices you must follow when using shielded N2 cable for this or any other noisy application 34 Introduction ASC and N2 Bus Networking and Troubleshooting Guide Rules for Using Shielded Cable Follow these rules and recommendations when using shielded cable for the N2 Bus Several examples that show these rules in effect follow this section e Hard ground the shield at the Panel LTD or PC Version Companion This is the only location that the N2 shield is hard grounded This makes it easy to check for a single ground with an ohmmeter by temporarily removing the shield at
41. s or cycle downloading the ASC has not yet power expired HVAC PRO Release 1 0 or earlier 24 Introduction ASC and N2 Bus Networking and Troubleshooting Guide TEST 1 Earth This test applies only to the VAV100 101 and UNT100 101 Controllers Grounded 24 only You ll need a 100K ohm resistor and a DMM to perform this test VAC Load Follow these steps 1 If you have a Companion PC Version remove the 25 pin RS 232 connection from the MM CVT101 converter This removes the fluctuating voltage due to communications and allows you to read the DC bias voltage Plug the converter into a 120 VAC source If you have a Companion Panel LTD connect the Panel to a 24 VAC source 2 Connect a 100K ohm 1 4 watt resistor across the DMM For easier installation insert a double banana plug into DMM 3 If you cannot guess which ASC may be causing the ground loop follow Steps 3a and 3b below If you suspect which ASC is causing the ground loop follow Step 3c on the next page a Connect one DMM lead to REF N2 or N2 and the other to earth ground Figure 12 Read the VDC VAC scale on the DMM If the value is greater than 1 VDC VAC a ground loop is present and therefore the N2 Bus is not properly isolated Subdivide the N2 Bus and measure again Continue to subdivide the bus until you locate the source of the problem Correct the isolation problem and measure again If the value is less than 1
42. tests you may be able to determine the cause of the problem by asking yourself the following questions e Are the N2 Bus wires securely terminated to each ASC e Is the N2 polarity correct e Is the ASC powered and ready to respond e Are the end of line device settings correct e Have you cycled power on an ASC after changing its address e Is the W3 loopback jumper on the Companion Panel LTD fully pushed down on pins 1 and 2 e Are the ASCs configured properly with the correct number of points The tests are designed to find opens shorts ground loops or crossed wires on the N2 Third this section describes the diagnostic LEDs on the AHU A CAUTION To avoid electrical shocks when troubleshooting always measure the REF to earth ground voltage with a 100K ohm resistor installed at the DMM If line voltage is measured have a qualified electrician locate the fault The tests covered in this section require the use of these components e Digital Multimeter DMM e 100K ohm resistor e 9 volt battery e red LED test light e 470 ohm resistor e oscilloscope Introduction ASC and N2 Bus Networking and Troubleshooting Guide 23 Troubleshooting Table 5 Troubleshooting Chart Possible Cause Action N2 Bus is EOL jumpers and or W3 jumper on Install EOL jumpers and W3 jumper offline MM CVT101 or Companion properly Panel LTD are not installed MM CVT101 is not plugged into Plug MM CVT101 into PC or plug it PC or
43. the Panel LTD or PC and measuring the N2 e Ifthe ASC is connected to earth ground soft ground the shield terminations of all other devices with a 560 pF capacitor Make this connection within one inch of the entry point of the enclosure If earth ground is not available connect the shields together or if only one shield tie back and leave unterminated e If several ASCs are installed in one enclosure soft ground the shield of the cable that enters the enclosure within one inch of the entry point You must make the shield continuous within the enclosure but do not earth ground it inside the enclosure e When you connect the shield through a 560 pF capacitor to an ASC in a metal enclosure terminate the shield on the metal enclosure at the point of entry with no more than one inch of shield exposed inside the enclosure Earth ground the metal enclosure e Use shielded wire for a sensor that has a noisy signal near it Hard ground the shield at the ASC and soft ground the shield at the sensor e If shielded cable is used and the ASC is in a grounded metal enclosure connect the shield at the entry to the enclosure through a 560 pF capacitor e If shielded cable is used and the ASC is not in a grounded metal enclosure connect the shield to earth ground if available Otherwise connect the shields together Introduction ASC and N2 Bus Networking and Troubleshooting Guide 35 Sample The configuration shown in Figure 16 indicates
44. troduction ASC and N2 Bus Networking and Troubleshooting Guide 5 ASC Installation Steps This section describes how to install ASCs The ASCs include the Air Handling Unit AHU Controller Lab and Central Plant LCP Controller Unitary UNT Controller and Variable Air Volume VAV Controller Notes These procedures are not required however they are recommended to reduce installation errors If you are fairly confident that the field wiring has no earth grounds you may skip Step 2 which instructs you to measure each field wire terminated to the ASC Skipping this step shortens the procedure If you skip Step 2 and a field device is earth grounded it will be caught in Step 5 when the entire ASC is tested 1 Mount the ASC in an appropriate location as described in its technical bulletin 2 Before terminating the field wires to the ASC measure the resistance of each wire to earth ground using an LED test circuit preferred or a DMM For the LED test circuit assemble the test circuit shown in Figure 2 Then connect the circuit from each input to earth ground and then to each output to ground For the DMM test connect the DMM from each input to earth ground and then to each output to ground Figure 2 If the LED turns On or you read a value less than I Megohm at any input or output the circuit is improperly isolated Replace or repair the wiring or the field device or for a binary output add an isolati
45. tween the two Quiet Wiring Wiring that is free of transients This wiring includes binary inputs analog inputs and outputs 24 VAC power and communication buses Noisy Wiring Wiring that is subjected to transients because of its proximity to sources of electrical noise or because of the loads to which the wiring is connected e g switched low voltage loads switched line voltage loads gas ignition and line voltage distribution Routing quiet wiring near noisy wiring requires that the quiet wiring is shielded Low voltage is defined as 24 VAC Line voltage is 120 VAC or higher We recommend that all ASCs are installed in enclosures especially in noisy areas The ENC100 or BZ1000 7 works well We also recommend that the enclosures are earth grounded Placing ASCs inside another piece of equipment which contains a metal housing e g a rooftop unit or a motor control center does not constitute locating the control device inside a quiet metal enclosure While the location may provide physical protection for the control device the presence of electrical noise makes it a noisy box Therefore always use a separate grounded metal enclosure for noisy environments Wiring the ASCs and other devices involves some type of grounding It is important to know the difference between the two types hard ground and soft ground Hard Ground an electrical connection to earth through a conductor such as steel or other metal A hard ground is
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