USER'S MANUAL
Contents
1. Way1 Way2 Way3 Percentage off X X 0 ON off off 6 25 ON off ON 12 5 ON ON off 25 ON ON ON 50 Switches 4 and 5 define the nominal trigger on threshold see section 3 2 3 2 Way4 Ways Threshold off off 0 8 off ON 1 6 ON off 0 2 ON ON 0 4 19 SL MD 220 User s Manual SENSCOUR LINE Switches 6 and 7 select the baud rate of the serial interface see section 3 2 6 2 Way6 Way7 Baud off off 9600 ON off 19200 X ON 115200 When Switch 8 is in ON position the trigger output on time is forced to a minimum value which depends from the setting of Jumper J1 see below 3 2 4 2 Jumper Settings When Jumper J1 is installed the minimum trigger output on time is 40 ms with J1 removed itis 20 ms This requires Switch 8 to be set to ON position see above otherwise the configuration of J1 has no effect Jumper J2 is reserved for future use 3 2 5 Status Outputs The status outputs are the six status LEDs and four optocoupler outputs on the system terminal block In spite of the common labeling of some of them their behavior is not the same This might be confusing at first but provides maximum convenience during operation 3 2 5 1 Status LEDs There are three groups of status LEDs TRGx AUXx and ERRx The TRGx LEDs show the trigger status of both channels the red ERRx LEDs report error conditions and the AUXx sho2. 77 F Temperature Range 40 C to 85 C 40 F to 185 F Supply Voltage 12 to 24 VDC Supply Current lt 140 mA Analog Output at Test Points 0 10 V Optocoupler Outputs max OFF 50V lt 1uA ON 5V 50 mA 250 mW 25 C RS 232 connector 9 pin DSUB male Velocity Range 1 to 250 km h 0 6 to 155 mph Feeder Length up to 250 meters 820ft EMV EMI Meets CE requirements LED Risk Group RGO safe According to DIN EN 62471 Please note In spite of the official classification SENSOR LINE recommends to avoid staring into the transmitter for longer periods regardless whether light is visible or not Software Program Name MD220STD Program Version 1 3 Program cycle time 500 us 5 Watchdog expiration time 4ms Triggering Thresholds 0 2 0 4 0 8 1 6 change of light transmittance Adaptive Threshold 0 6 25 12 5 25 50 of load signal Hysteresis 2 digits Minimum input ON time 3 program cycles 1 5 ms Minimum output ON time 3 program cycles 1 5 ms 40 program cycles 20 ms 80 program cycles 40 ms Maximum output ON time 30s RS 232 Baud Rate 9600 19200 115200 Bd Data Bits 8 Stop Bits 1 Parity N no parity selectable with jumper J1 selectable with SIL switch SL MD 220 User s Manual SENSCOUR LINE 2 Hardware Section The PCB version is found on th
3. supply The MD 220 has built in voltage regulators and is reverse voltage protected The interface draws a maximum of 140 mA Connect the negative output to Terminal 1 and the positive output to Terminal 0 SL MD 220 User s Manual SENSCOR LINE 2 4 2 2 Optocoupler Outputs 2 4 2 2 1 Internal Circuitry 100 Ohms 0 25W O Terminal H11G1 Optocoupler o Terminal The above schematic shows the internal circuitry of the TRG1 amp 2 and AUX1 amp 2 optocoupler outputs When the phototransistor is illuminated by the LED ON condition current flows into the terminal and out of the terminal The resistor limits the maximum allowable current to 50mA Therefore any DC voltage applied directly to the outputs must not exceed 5V when the phototransistor is conductive because the maximum power the 100 Ohm resistor can dissipate is 250mW When the phototransistor is not conductive the maximum voltage is limited by the zener diode to 68V If a voltage above that value is applied even with additional resistors the output might appear conductive but the phototransistor is not To avoid any glitches caused by voltage spikes or surges the optocoupler outputs should not be operated with voltages above 50V 2 4 2 2 2 External Wiring The optocoupler outputs are not connected to any voltage source so there are many ways to obtain various kinds of output signals In all cases an external power supply must be added The outputs behave as
4. as the SIL switch see above by installing jumpers or connecting external switches They can also be used as UO connections for various purposes Please refer to the software section of this manual for more information 12 SL MD 220 User s Manual SENS oJR LINE 2 9 Status LEDs There is a display of six LEDs controlled by the microcontroller TRG1 TRG2 AUX1 and AUX2 are yellow and ERR1 and ERR2 are red Please refer to the software section of this manual for the meaning of the LED signals 2 10 Measuring Pins me ALEN LEX There are five test points with 1 3mm 0 05 pins for measuring the analog voltages evaluated by the microcontroller The meaning of these voltages is thoroughly explained in paragraph 1 2 on page 4 Label GND MONI ANA1 MON2 ANA2 Signal Ground Monitor Voltage Channel 1 Analog Voltage Channel 1 Monitor Voltage Channel 2 Analog Voltage Channel 2 Sign VMon1 VANA1 VMon2 VANA2 13 SL MD 220 User s Manual SENS OR LINE 2 11 Fiber Optic Receptacles Two fiber optic load sensors can be connected to the MD 220 via four SMA 905 fiber optic receptacles Viewed from the front the receptacles for Channel 1 are on the left hand side and those for Channel 2 on the right hand side The transmitters are the inner receptacles Do not stare into the transmitters when the interface is powered and there is no sensor connected Fasten the sensor s fiber connectors to t
5. condition regardless at what channel 3 2 5 3 Status Table The table below is to summarize the different states the two channels can be in and the according behavior of the status outputs Status Status LEDs Optocoupler Outputs Channel1 Channel2 TRG1 TRG2 AUX1 AUX2 ERR1 ERR2 TRG1 TRG2 AUX1 AUX2 adjust Adjust 2 flash flash adjust Ready ON flash adjust Detect flash ON adjust Error 2 ON flash ON ON ready Adjust ON flash ready Ready ON ON ready Detect ON ON ready Error ON ON ON ON detect Adjust j flash ON detect Ready ON ON detect Detect ON ON ON ON detect Error ON ON ON ON error Adjust ON ON flash ON error Ready ON ON ON ON error Detect ON ON ON ON error Error ON ON ON ON may flash during startup 21 SL MD 220 User s Manual SENSCOUR LINE 3 2 6 RS 232 Interface 3 2 6 1 General The RS 232 interface of the MD 220 allows bi directional communication with a host computer or a passive RS 232 device It can be used for debugging and troubleshooting purposes as well as for setting up simple measuring systems Please refer to paragraph 2 5 for the wiring of the connector 3 2 6 2 Comm Parameters The baud rate of the MD 220 s RS 232 interface is adjustable to 9600 19200 and 115200 Baud The remaining parameters are 8 N 1 8 data bits 1 stop bit no parity The higher baud rates may
6. load for infinite time If during load detection the amount of light detected without any load drifted below the stored threshold the interface would no longer be able to notice the load being removed it would hang For this reason there is a maximum detection time of 30 seconds When this time has elapsed the interface performs an initialization process similar to the one at startup The interface is then ready to detect additional load being applied to the sensor The original load effect is regarded as intrinsic sensor attenuation When the original load is removed the threshold is adapted immediately When the sensor is broken or disconnected no light arrives at the receiver and the interface is unable to detect any load If the sensor fails during operation the detected light falls below the threshold and is reported as load being detected Therefore sensor failure during operation is first reported as a load detected and it changes to an error signal after 30 seconds 15 SL MD 220 User s Manual SENSCOUR LINE 3 2 Details 3 2 1 Startup Procedure After power up or when a program reset is initiated the MD 220 first tries to adjust itself to the particular sensors attached This process takes about one second and is signaled by both ERRx LEDs see paragraph 3 2 5 1 on page 20 flashing at 8 Hz If insufficient light is detected i e if there is no sensor connected to a channel or the connected sensor is broken the respe
7. t ora T is received the MD 220 continuously reports the sensor transmittances with two four digit hex numbers every line The message format is XIX X X X X X X CRILF Dag Q Q Q SHES oO oO es SI nes cis ogc S cose Sl sen Z see GG OD lt GG D X CT CT 0 OSs Ss OSs Fe oO Unlike the logarithmic sensor loss which is given in dB and signaled by the TRGx LEDs on startup the sensor transmittance is a linear quantity which is given in arbitrary units here The theoretic dynamic range of the interface is represented by values from 4h 4 to D8Fh 3471 It must be noted that errors are not signaled exactly when these values are exceeded because the conditions which define an error are not derived from this quantity 23 SL MD 220 User s Manual SENSCOUR LINE 3 2 6 3 4 Status Mode This is a non continuous output mode It is entered on receipt of an s or an S The status of each channel of the MD 220 is internally described by two status bytes Every time one of these four bytes changes a status message is issued The message format is xX X X X X X X X X 1X X X X X CRILF ae 5 3 e z e gen d E 3 T HS EI e 5 ec CN a e H E ojl pus S e oC 5 I N xe N 5 N 5 EE 2 cox cox E x Q x x Yo 6 2 o D C oj D C BHD LL OO bo Che be 7 0 co 0 0 Zo al o s O x oi H x e CAE
8. 5 3 2 Detail S serune en ENNEN e Ea 16 3 2 1 Startup Frcedure vi 2 i c ccscnsessdscnecssanienedssvcnesessseeseasdvarensddtsuansdanauensdacioasedansnens 16 322 MMI EE 17 3 2 2 1 Program oeleime a 17 3 2 2 2 Watchdog Ri Un EE 17 SL MD 220 User s Manual SENS JR LINE 557265 Ban USN E ET 17 329 1 Tigger EMI E 17 3 2 3 2 Nominal Trigger Threshold 2 22 22 2 sr 17 3 2 3 3 Adaptive Trigger Threshold enenenene nennen 18 3 2 4 SIL Switch and Jumper Settings AE 19 3 2 4 1 Switch Settings ee ee ee 19 3 2 4 2 Jumper din E 20 3 2 Status TE 20 E NEE e 20 3 2 5 2 System Terminal Block ANNE 21 3 2 5 3 Stat s Table EN 21 3 20 RS 232 Ee Le 22 E Re ER 3 2 6 2 Comm barameiers retrete 22 3 2 03 ue Modes sun anne nern 22 KA Ne le CT ER 3 2 6 3 2 Percent Mode 23 3 2 6 3 3 Transmittance Mode nn 23 SS Stat s e 24 3220 9 OTT dE 25 3 2 6 3 6 Software Version Query ENEE 25 Ee innnniuisnitaenle ee 25 3 2 6 3 8 Special Output Modes ann ennenen nenne nennen ennnen nenene nennen 25 3 2 6 4 nn En sisasaivnrnextphnriecsendetdiecteisahaswesdenachesnctateeedcanshessaniintedanasmetenmeiaaeadieatoes 26 3 2 6 4 1 System Reset Commande 26 3 2 6 4 2 Threshold Reset Command u 26 SL MD 220 User s Manual SENSCOUR LINE 1 General 1 1 Introduction The SENSOR LINE MD 220 is a two channel static opto electronic interface for SENSOR LINE s SPZ SPT fiber optic load sensors This two channel interface supplies light to two fiber opt
9. HIGHLOSS Sensor loss above dynamic range Error Bit 13 SENSOR_LOWLOSS _ Sensor loss below dynamic range Error Bit 14 reserved Bit 15 MSB reserved The very first status message is transmitted immediately after entering status mode but this does not mean that something has changed at that moment Every additional s or S triggers a new message without status change 24 SL MD 220 User s Manual SENSCOUR LINE 3 2 6 3 5 Off Mode On receipt of an o an O or a 0 zero the transmission of any messages is inhibited The interface still receives characters and can be switched to another mode at any time 3 2 6 3 6 Software Version Query When the MD 220 receives a q or a Q a short copyright notice including name and version number of the loaded software is issued Enter off mode or status mode before querying the software version 3 2 6 3 7 Fast Mode Fast Mode was formerly one of the special output modes addressed in section 3 2 6 3 8 Since it has repeatedly been applied in the field some more detailed discussion is adequate The MD 220 enters Fast Mode on receipt of a capital E This is a continuous output mode where the analog voltage readings see section 1 2 of both channels are converted into strings of two printable characters each and transmitted without any delimiter Every 76 characters a CRLF sequence is inserted mainly for the purpose of synchronization but also to
10. SCOR LINE Our product guides and instructions are continuously updated Make sure you have got the latest edition For further information contact the SENSOR LINE technical support team OT
11. SENS R LINE Optical Transmittance Analyzer SL MD 220 USER S MANUAL Hardware Version 2 0 Software Version 1 3 SENSI R LINE Sensor Line Gesellschaft f r optoelektronische Sensoren mbH Carl Poellath Str 19 D 86259 Schrobenhausen Germany Tel 49 0 8252 8943 0 Fax 49 0 8252 8943 11 Email sensorline sensorline de www sensorline de SL MD 220 User s Manual SENSCOUR LINE Table of Contents 1 GOMO all E 4 1 1 Tit ele Leide bait tien dei eens reese DM A ees 4 1 2 Principle Of Operation anni 4 1 3 Technical Data 6 2 Hardware Section uuun44444nnnnnnnennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnennen REENEN 7 2 1 Dimensional Drawing cay na a at 7 2 2 Handling lt CN 7 2 3 installation ME 8 24 System Terminal eier 8 2 4 1 Mechanical 8 2 4 2 Connechons sn 8 2 4 2 1 Power Supply Terminal 8 2 4 2 2 Optocoupler OUND UNS scincis nannten anne nern nenne 9 2 4 2 2 1 EE eg 9 24 222 External Wiring WE 9 2 4 2 2 2 1Generating Voltage Output Signals 4444ssnnnssnnnnnnnnnnennnnnnnn 9 24222 2DNVNJ E zn ee 10 2 5 En na ahnen nn aaa insisi sesin 11 23 1 e E 11 22 MINING EE 11 2 6 Reset Switch WER 12 27 EE 12 2 8 JUMDELSesrEE e a A LEER N DEE ES ner 12 29 Statue LEDS n ieeeguele eine eegene ne 13 2 10 Measuring PINS E 13 2 11 Fiber Optic Receptacles AAA 14 212 JTAG CONNECtO eaae ine EE eege toed 14 3 Software SS CHO Mc nn 15 3 1 e Eeler EE 1
12. ain 3 2 6 3 8 Special Output Modes When one of the characters C Y or Ctrl q Chr 17 is received the interface enters special output modes which are meant for laboratory use or troubleshooting in special cases The output consists entirely of printable characters but special software is required to decode it 295 SL MD 220 User s Manual SENS OUR LINE 3 2 6 4 Commands Aside from the previously described characters which only change the output sent via the RS 232 interface there are also characters which directly affect the behavior of the MD 220 3 2 6 4 1 System Reset Command On receipt of a capital R a software reset is initiated just as if the reset button had been pressed This is done by sending the controller into a non terminated loop and having the watchdog timer trigger the reset Consequently it may take up to 4 ms until it is executed This command can also be used to verify the watchdog function 3 2 6 4 2 Threshold Reset Commands When the MD 220 receives a 1 or a 2 the trigger threshold of the respective channel is immediately reset This must not be confused with a system reset which causes the complete startup initialization process to be performed Here the interface only accepts the current light level as new no load value and establishes its trigger threshold 0 2 0 4 0 8 1 6 below it The threshold management algorithm used with MD220STD v1 3 is sophisticated This can not keep the int
13. ctive ERRx LED comes on continuously along with the AUX2 LED The AUX2 optocoupler output becomes conductive and the associated TRGx LED flashes ten times at 2 Hz The TRGx LED is then switched off In the case that there is too much light detected which may happen when an interface with infrared transmitters is used in conjunction with a low loss sensor the ERRx and AUX2 LEDs and the AUX2 optocoupler outputs behave the same way but the TRGx LED does not flash If the sensor loss is within a range where the interface can successfully adjust itself the program waits for the transmitter to stabilize its output power This is necessary because during power up the transmitter becomes warm causing a slight decrease in its brightness during the first few seconds Since it is not possible to derive a measure for the sensor loss from the analog voltages at the test pins the interface signals the virtual sensor loss during warmup time It cannot determine the real sensor loss Rather the sensor loss in this cases defines a certain value within an internal theoretic dynamic range of 30 dB For a number of reasons this range can not be fully utilized in practice but the interface sees the loss of the sensors vary within it In order to express this virtual sensor loss the internal dynamic range is divided into ten intervals of 3 dB While the transmitter is warming up the TRGx LED of each channel is flashed from one to ten times The number of times i
14. d should never be touched The test points are connected to OP outputs which are also sensitive to ESD Discharge any measuring clips on the GND pin before contacting one of the other test points SL MD 220 User s Manual SENS JR LINE 2 3 Installation The MD 220 PCB has four 3 1mm 0 12 through holes allowing it to be mounted on any appropriate flat surface by means of M3 screws At least 5mm 0 2 spacers are recommended to ensure a sufficient gap between the PCB and the mounting surface 2 4 System Terminal 2 4 1 Mechanical The system terminal is a 10 wire screw terminal block which accepts 0 14 1 5 mm 26 16 AWG wires To fasten the screw clips a screwdriver with a blade up to 3 5 mm wide can be used The terminal block can either be a flat or angled design the latter is used if several interfaces are stacked 2 4 2 Connections Pinning Sign Description o 12 24VDC Supply Voltage 4 O GND Ground at AUX2 Auxiliary Optocoupler Output 2 3 O AUX2 Low Resistance Sensor Failure 4 AUX1 Auxiliary Optocoupler Output 1 5 O AUX1 Low Resistance TRG1 AND TRG2 6 TRG2 Trigger Channel 2 Optocoupler Output 7 TRG2 Low Resistance Load Response D TRGI Trigger Channel 1 Optocoupler Output 9 TRG1 Low Resistance Load Response 2 4 2 1 Power Supply Terminal Terminals 0 and 1 of the system terminal block are for connection of a 12 24 VDC power
15. e bottom layer of the PCB This manual is for hardware version 2 0 2 1 Dimensional Drawing 110 4 331 JTAG s Connector Tt IQ 12 24VDC E GND Channel 1 _ Eier D D Receiver E io AUX2 Q Through Holes 3 1 122 E ei o AUX2 S 5 Fils Mik Channel 1 e el ve UO AUX1 ale Transmitter 2 ei o UO TRG2 Pe 18 gt Hin I TRG2 pe le o 4 2 S x A O TRG1 e as Channel 2 Hito TRG1 o Transmitter amp 5 RS 232 2 Channel 2 Connector Receiver SIL Switch Jumpers f m H GND MON ANA1 MON2 ANA TRG1TRG2 AUX1 AUX2 ERR1ERR2 J2 Ji RESET Test Points Status LEDs Reset Switch 120 4 724 Maximum Height 19 748 Dimensions in mm in 2 2 Handling Precautions The MD 220 is delivered without a housing so handle it the same way as a PC card Some of the interface components are sensitive to electrostatic discharge ESD Leave the interface inside its conductive bag until installation Discharge yourself by touching a grounded conductor before touching the interface The receptacles are either non conductive or grounded and the system outputs have a special protective circuitry It is relatively safe to handle the interface by these parts If conductive spacers are used the interface may be handled by these spaces because the rims of the through holes are also grounded Before pressing the reset switch by hand first discharge yourself The jumpers and LEDs are connected directly to the controller an
16. erface from hanging if during load detection something reduces the sensor s transmittance permanently The trigger signal will then remain on for 30 s and the interface will be unable to detect any new load cycle during this time The threshold reset command enables a host computer to tell the MD 220 that there is currently no load on the sensor This is useful to clear the trigger signal in situations where the interface is suspected or known to be hanging The command can also be given by the host computer if it knows there can be no load on the sensor from another detector i e a inductive loop Using this feature will make malfunctions or anomalies virtually impossible The command should not be used to acknowledge a trigger signal by clearing it since the load may not have reached its maximum value yet If the trigger threshold is reset while the load increases a second trigger signal might be erroneously generated by the still increasing load Important notice All the information contained herein is believed to be accurate and reliable However SENSOR LINE assumes no responsibility for its use or for any infringements of patents or other rights of third parties that may result from its use No license is granted by implication or otherwise under any patent rights of SENSOR LINE GmbH SENSORLINE shall not be liable for any special incidental or consequential damages related to the use of the product 26 SL MD 220 User s Manual SEN
17. essing can be switched on and off The ratio of signal amplitude to which the trigger threshold adapts can be defined to values of 50 25 12 5 and 6 25 Please refer to section 3 2 4 for instructions 18 SL MD 220 User s Manual SENSCOUR LINE 3 2 4 SIL Switch and Jumper Settings Important Notice The settings of the SIL switch as well as those of the jumpers are only read at startup Thus putting any changes into effect always requires a startup process to be executed This can be initiated by pressing the reset button on the board but also by powering the interface down for a moment or issuing an R command via the serial interface Failing to do so will leave the MD 220 s behaviour unchanged 3 2 4 1 Switch Settings Both boards have an 8 way SIL switch immediately behind the display LEDs The particular switches are numbered from 1 to 8 where switch 1 is the leftmost one They are in on position when swiveled towards the front edge of the board i e towards the LEDs Factory setting is all switches off Switch Functions a N w gt a D N Adaptive Threshold Enable Adaptive Threshold HI Adaptive Threshold LO Trigger Threshold HI Trigger Threshold LO Baudrate Select High Speed Enable Enforce Minimum Pulse Duration Switches 1 3 set the percentage to which the trigger off threshold follows an input pulse adaptive threshold see section 3 2 3 3
18. facilitate display with terminal programs By this a very high repetition rate is obtained which is necessary to resolve sensor signals also with faster moving traffic The algorithm which converts the signal values to printable characters is derived from the common uuencode algorithm but not compatible so special software is needed to decode the output When working with Fast Mode two things must be considered First the values of the monitor voltage and the trigger threshold are not transmitted as they are in Voltage Mode This yields some much higher measuring frequency but without knowledge of these quantities neither computation of the relative sensor signal nor deduction of the trigger signal is possible So if Fast Mode data are to be of any value they must be accompanied by a short sequence of Voltage Mode messages captured under the same circumstances without traffic Second due to the high measuring rate the amount of accumulating data grows very fast Fast Mode is therefore absolutely inadequate for any kind of long term logging purposes Its output can only be processed without major problems if it consists of short sequences it is virtually impossible to isolate interesting events from megabytes of logged traffic So the best way to utilize Fast Mode is first capturing some lines in Voltage Mode then switching to Off Mode invoking Fast Mode immediately before an interesting event and immediately afterwards shutting it down ag
19. ge of light transmittance Please refer to section 3 2 4 for instructions 17 SL MD 220 User s Manual SENS JR LINE 3 2 3 3 Adaptive Trigger Threshold Adaptive threshold processing is a trigger algorithm introduced with Version 1 3 of MD220STD It is intended to be applied in cases where sensors show a noticeably delayed relaxation process Behaviour of this kind can encumber certain signal processing methods for dual tire detection or automatic vehicle classification which rely on correct registration of the load pulse duration In extreme cases it can even cause the trigger output to hang after a tire has left the sensor This issue is overcome by the adaptive threshold algorithm After the trigger event has happened the trigger threshold follows the sensor signal with a certain fraction of its amplitude as long as the amplitude is growing i e the sensor transmittance is decreasing When the sensor transmittance rises the threshold is held constant until the trigger state has switched to OFF again After that the threshold is held at a level below the sensor signal which complies to the nominal threshold value according to section 3 2 3 2 as long as the sensor transmittance is not decreasing again Adaptive Threshold Fixed Threshold 100 d Es g a o S 5 D a E 5 5 8 E Sensor Signal o g D F 2 5 0 o ON Output Pulse Output Pulse with Adaptive L abe Threshold OFF Time Adaptive threshold proc
20. he transmitter or receiver by screwing tightly on by hand the tighter the smaller the attenuation DO NOT USE PLIERS The transmitter and receiver connectors are interchangeable for each channel The transmitter connectors are not interchangeable i e a sensor connected for example to Transmitter 1 and Receiver 2 will not work 2 12 JTAG connector D H D oO Ke go 52 The JTAG connector is used for programming the microcontroller at the factory If you are intending to re program the device in the field please contact Sensor Line GmbH for further information 14 SL MD 220 User s Manual SENSCOUR LINE 3 Software Section The following refers to the MD 220 program MD220STD version 1 3 3 1 General Description The program executed by the microcontroller controls all functions of the MD 220 Detecting a load applied to the sensor is difficult because of the large variation in sensor transmittance versus the small amount of transmittance change when load is applied For example ifthe sensor transmittance could change by a factor of 100 20 dB and the transmittance change caused by a load was 1 1 100 the complete light measuring range would have to be resolved to 1 10000 of its value in order to detect the load This is more than twice the resolution of a 12 bit ADC To overcome this difficulty the microcontroller controls the photo currents detected by the input amplifiers in two ways First it can vary the tran
21. ic sensors monitors the amount of light transmitted through the sensors and detects small changes caused by loads applied to the sensors With its advanced circuitry the interface can detect a load on a sensor for as long as it is applied to the sensor The MD 220 incorporates a TI MSP 430 embedded microcontroller programmable via a JTAG interface It has a 10 wire screw clip interface with power supply terminals and four floating optocoupler outputs It also has a RS 232 interface for input and output of data Direct external control is possible through the use of an 8 way SIL switch two jumpers and a reset switch For quicker troubleshooting six LED status displays show the function of the interface and there are five easily accessible test points for analog measurements Power consumption has been minimized by circuitry that operates the transmitter diodes in series while independently controlling the current through each diode The MD 220 comes with two different kinds of transmitter diodes a near infrared diode giving each channel a dynamic range of 30 dB and a more economic red diode for a dynamic range of 20 dB The hardware and software for the MD 220 come in different versions This manual is divided into a hardware and a software section Please ensure that you have the correct version of this manual 1 2 Principle of Operation GND GND The drawing above is a simple circuit diagram of one channel When the photodiode is illum
22. imer is serviced every time the main loop is executed Its time interval is set to 4 ms If the program hangs for whatever reason and this time expires a program reset is performed 3 2 3 Triggering 3 2 3 1 Trigger Timing The trigger function works with a threshold that has a hysteresis of only 2 digits This is just sufficient to prevent the interface from bouncing due to the sheer quantization error of the ADC Debouncing is done by requiring a valid load pulse to have at least 3 program cycles 1 5 ms of duration This requires that the trigger delay also be 1 5 ms The output pulse duration is correct because switching off and on is subject to the same conditions Optionally the output pulse duration can be forced to a certain minimum value regardless of the input pulse duration The output will then be on for at least that minimum time 20 ms or 40 ms in this program version Otherwise the output pulse duration can become as short as 1 5 ms Please refer to section 3 2 4 on how to define the minimum output pulse duration The maximum output pulse duration is 30 s This is the maximum detection time explained in paragraph 3 1 After 30s the interface is freshly adjusted and ready to detect a new load 3 2 3 2 Nominal Trigger Threshold Before introduction of hardware version 2 0 the trigger threshold was a fixed value and adjustment required re programming MD220STD v1 3 allows to select threshold values of 0 2 0 4 0 8 and 1 6 chan
23. inated with light from the sensor it proportionally sinks a current to the incoming light power This causes the output of the OP to go high so the current is supplied across the 7 5M resistor When the light becomes too bright the OP output is clipped and the controller supplies additional current via the DAC and the 470k resistor until the OP output is unclipped Small changes of photo current are amplified by the OP by a factor of 7 5 MQ 7 5 V uA The controller measures this voltage Analog Voltage or Vanax as well as the voltage 4 SL MD 220 User s Manual SENS OUR LINE produced by the DAC Monitor Voltage or Vmonx with a resolution of 12 Bits An additional DAC controls the light power fed into the sensor Both voltages can be measured at test pins Since the sensitivity of the photodiode is about 0 5 A W the incoming light power can at any time be calculated using the formula WW Vmon anas 2 Ze Yan SL MD 220 User s Manual SENS IR LINE 1 3 Technical Data Device Type MD 220 Hardware Hardware Version 2 0c STD 1 Number of Channels 2 Size 100x110x19 mm 3 54x4 33x 75 in Electrical Connections 10 wire screw terminal block RS 232 3 wire 5 test points Optical connections SMA 905 LED Peak Output Wavelength 850 nm NIR 660 nm VIS red Maximum Sensor Loss 30 dB NIR 20 dB VIS Relative Humidity 80 at 25 C
24. je O The first 3 digit hex number gives the number of seconds elapsed since the last reset It is reset to zero every hour its maximum value is EOFh 3599 The second number is the number of milliseconds which is zeroed when the second count changes Its maximum value is therefore 3E7h 999 The following two 4 digit hex numbers give bit wise information about the status of each channel Their meaning is as follows Bit0 LSB TRIGGERED Channel is currently detecting load trigger signal is on Bit 1 TRG_TIMEOUT Trigger signal has been on for 30 s and will now be cleared trigger threshold will be reset Bit 2 TRG_INHIBIT Trigger signal inhibited Bit 3 reserved Bit 4 ANALOG_LOW ANAx voltage requires upward adjustment Bit 5 ANALOG_HIGH ANAx voltage requires downward adjustment Bit 6 ANALOG_DOWN ANAx voltage too low for proper triggering Error Bit 7 ANALOG_CLIPPED ANAx voltage too high for proper triggering Error Bit 8 THRSH_NOUPDATE Updating of trigger threshold is inhibited due to expected load detection Bit 9 THRSH_TIMEOUT Trigger threshold has not been updated for 30 s and will be updated now Bit 10 THRSH_RESET Trigger threshold is considered to be wrong and will immediately be set to 0 2 0 4 0 8 1 6 below current light level Bit 11 THRSH_NINIT Trigger threshold not initialized trigger signal inhibited Bit 12 SENSOR_
25. marked as text format otherwise numbers that do not contain any letters will be imported as decimal numbers 22 SL MD 220 User s Manual SENSCOUR LINE 3 2 6 3 2 Percent Mode Percent mode is entered as soon as the MD 220 receives a p or a P It continuously reports the relative difference of the registered light power to that which is related to the currently established trigger threshold The message format is 1X X X X X 1X CRILF en ls Lef 8 SE _ 55 E _ 9 55 ES SICH Iel igo E 35 lee2 Z lesoe2 ejg 022 E Ee S mp OH D OH oO clog alsog o D oo Ei oon olge oi D ol X E15 D O The values are given in units of 0 1 For example if the trigger threshold is set to 0 8 the values issued should be around 008 As soon as the sign changes to the interface will trigger This output mode allows for quick judgment of the measuring effect especially the quality of the sensor setup on site without any computations The signal resolution is significantly lower than that obtained from voltage data but the messages are shorter so there is a higher time resolution in percent mode 3 2 6 3 3 Transmittance Mode With this output mode a host computer checks the loss of connected sensors This cannot be derived from the analog and monitor voltages alone because these do not contain any information about the light power fed into the sensors When a
26. not be available especially with older RS 232 PC interfaces However with an USB to RS232 adapter they should work without problems 3 2 6 3 Output Modes There are several different possibilities to output useful data via RS 232 Switching between these output modes is done by sending single characters to the MD 220 The easiest way to do so is by using the keyboard on a PC running a terminal program 3 2 6 3 1 Voltage Mode The Voltage Mode is the default mode at startup While operating in another mode the MD 220 enters the Voltage Mode when it receives a v or a V The interface then continuously reports its analog voltages monitor voltages and thresholds The message format is X X X XIXIX XIXIX XIXIX XIXIX X X IX CRILF aig lt Oo kej o 2 o o 5 Q CH fo fo ke Cake oye NX CIN D IND CDN NM Cc _ se S L ao ele 22 5 93 S 2 EIS oos o LE le Ee aloof Nlo SL IN fen hf Cc wel EL we LE ce xic se 1 Ek 2 we LE KG X o DD COD mgi Elo D Ele oD e E e LL ZS o mi oO SES Su Ss oo oe Sen 299 52955 2198 129 Bo SO 50 Rg MH be O All voltages are given in 12 bits ADC digits with a maximum value of FFFh 4095 corresponding to a voltage of approximately 10V This output can be logged and later processed into suitable diagrams When reading it into Microsoft EXCEL all fields must explicitly be
27. riving a LED 10 SL MD 220 User s Manual SENS R LINE 2 5 RS 232 Interface The MD 220 has a three wire RS 232 interface with a male 9 pin DSUB RS 232 connector It behaves like a PC sending data on the TXD line Pin 3 and receiving on the RXD line Pin 2 It can be connected directly to a printer with a standard RS 232 cable To connect it to a PC anull modem cable is required similar to the connection between two PCs Please refer to the software section for communication parameters as baud rate parity etc 2 5 1 Connector 2 5 2 Wiring RS 232 device Female Connector Male Connector Standard RS 232 Cable MD 220 PC 5 GND 1 Female Connector Female Connector Null Modem Cable 11 SL MD 220 User s Manual SENS OJR LINE 2 6 Reset Switch Pressing the reset switch causes a hardware reset of the microcontroller The two pads next to the right of the switch are connected in parallel and can accept a two pin header to allow for connection of an external switch 2 7 8 Way SIL Switch TRG1 TRG2 AUX1 AUX2 ERF The SIL switch consists of eight individual switches which are connected to I O pins of the microcontroller They are used to signal different conditions in order to modify the behavior of the interface without re programming it Please refer to the software section of this manual for the different switch settings 2 8 Jumpers The headers J1 and J2 can be used for the same purpose
28. smitter currents by a factor of ten Second it can subtract an offset of up to 16 times the range of the amplifiers from their input current With growing sensor transmittance the light power fed into the sensors is reduced in order to avoid clipping of the signal When the minimum value is reached the controller compensates for further increases in sensor transmittance by subtracting increasing portions of the photo current before the remainder is fed into the amplifiers see paragraph 1 2 on page 4 After startup the program uses these methods to adjust the amplifiers output voltages called analog voltages to a value in the upper region of the ADCs measuring range Then it establishes a threshold below that value corresponding to a constant fraction of the light detected After this initialization process the program enters its main loop Here it monitors the analog voltages and checks if they have dropped below the threshold values thus signaling load being applied to the sensors As long as there is no load detected the thresholds are carefully adapted to slow changes drifting of the detected light and the analog voltages are adjusted if necessary However if there is load this process cannot be continued since it is impossible to determine whether a change of the detected light is due to drifting or due to a change of the load As equipment does not stop drifting when there is load on the sensor the interface cannot be allowed to detect
29. switches with the restriction that current can only flow in one direction Below are examples of how the outputs may be wired 2 4 2 2 2 1 Generating Voltage Output Signals Voltage output signals are required if high impedance inputs like those on an oscilloscopes are connected The wiring from the diagrams below can be used if the voltage from the available source has the required value or is not critical Terminalo Terminal Terminal c Terminal Zero output voltage going Positive output voltage going HIGH on ON condition LOW on ON condition SL MD 220 User s Manual SENS OUR LINE If the voltage available is too high for the intended inputs a second resistor must be added in order to create a voltage divider as given in the schematics below It is generally safe to choose resistors in the range of 10kQ Terminal Terminal Terminal Terminal Zero output voltage going Positive output voltage going HIGH on ON condition LOW on ON condition 2 4 2 2 2 2 Driving Loads When there are no high impedance inputs that inhibit the flow of current it is not necessary to generate a voltage In this case the optocoupler output can be used as a switch to turn current on and off The wiring below shows how to operate an LED or drive optocoupler inputs or relays The current must be limited to a maximum of 50mA with an appropriate resistor R Terminal j Terminal LED aw D
30. t flashes multiplied by 3dB is the virtual sensor loss If a sensor has high loss the transmitter needs more time to warm up because it is operated at high power The number of times the TRGx LEDs flash can not be directly translated into sensor loss since it is given with respect to that particular channel s dynamic range Dynamic range may vary due to variations of the opto electronic components However it shows how that particular sensor is handled by that interface channel If the TRGx LED flashes at least two times and no more than nine times during the warmup time there is at least a 3 dB reserve and operation can generally be considered to be safe regardless of the exact sensor loss and the particular interface used As long as the sensor loss is signaled by flashing TRGx LEDs the ERRx LEDs continue flashing at 8 Hz showing the warmup time has not yet expired and the interface is not yet operational After the ERRx LEDs are switched off and the TRGx LEDs are continuously on the startup process is complete 16 SL MD 220 User s Manual SENSCOUR LINE 3 2 2 Timing 3 2 2 1 Program cycle time The main loop of the program is executed during a constant time interval of approximately 500 us This time can vary about 5 due to the tolerance of the clock oscillator All quantities are updated at every cycle The time resolution of the interface is therefore equal to the program cycle time 3 2 2 2 Watchdog Timer The watchdog t
31. w other conditions or events The TRGx LEDs correspond to one channel each During initialization when the interface is adjusting itself they are flashing up to ten times giving a measure of the sensor loss see also paragraph 3 2 1 on page 16 They are on if the respective channel is ready to detect load and go off when load a load is detected or when an error occurs The ERRx LEDs are also associated to one channel each During initialization they are flashing If the controller cannot transmit enough light through a sensor the respective ERR LED is switched on continuously The AUX1 LED is on when both channels are detecting load otherwise it is off The AUX2 LED comes on when either of the channels has an error condition and its ERR LED is on continuously This might seem redundant but the AUX2 LED is switched on and off in accordance with the AUX2 optocoupler output which reports an error see below This is convenient for troubleshooting purposes 20 SL MD 220 User s Manual SENS JR LINE 3 2 5 2 System Terminal Block The system terminal block has four optocoupler outputs divided into two groups TRGx and AUXx The TRGx outputs become conductive ON condition when there is load detected by the respective channel This is inverse to the TRGx LEDs The AUXx optocoupler outputs follow the AUXx LEDs The AUX1 output comes on when both of the TRGx outputs are on and the AUX2 output comes on when there is an error
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