CO2 Sensor User's Guide
Contents
1. SWITCHING SENSING TECHNOLOGY CO2 Sensor User s Guide CO2S A CO2S W CO2F W l Serial Formatand Connection eee ceri e eR eene EE Ae vals aain aiii 3 1 1 COMME GUON EE REIR DEATH M 3 1 2 Serial COnFectiOrn 2 2 deerit aes idonee sae aaro ese se Eod ga ab diee aee iE Des eae Eod Rash cdeades st a 3 1 3 Reading Format etos oet sedent eet ae oo ede seo o ae er qaae gena dece ye esu aaea Eene 5 1 3 1 CO5 Meeasurerient eei cote poct o eese c cba aco See rao pec Lc us S e a aa Dose SRek Us aE EE PEE DRE et pide 5 1 3 2 Temperature Measurement Option ccccccccsscccceesssceceessececeesseeeceeseeeeceeaeeeeeeeeeeeees 5 1 3 3 Humidity Measurement Option esseessessseeeeeeeee nennen nnne nnns nnne 6 1 3 4 Example of T Hand COsii ccccccccissseseeasestcccssesedvessestcestsoseessnsccteeciuessdussacsecesiueseesssecsesesaassys 6 2 Command SUMMARLY er ERE rone SEROREN Mar Fue eu Eusgn ae RN Vsus eus Se ERR SEERE 7 3 Operating MORES serei ecse eaa EA rete Eprv guste uin aE EEE osa ane VASE raai 8 3 1 Mode 0 Command Mode sss sees eene nennen nennen ns essent nennen nan 8 3 2 Mode 1 Streaming Mode sees nnne nnns enne neni in nasse isses tia iarsan 9 3 3 Mode 2 Polling MOdC cc cccccccsssssessnsecesccesessessesecececsseeseaeaesececsseeseaeaeeeesesseesesaeaeeeseesseeees 9 A QUE Fields ree enm a eve ues od 9 b Zero Point Calibration irit der Ra eo E Ke ue ERR NAT SRM e Ue2. O 2013 SST Sensing Ltd 13 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Note that the autocalibration timers are reset when the power to the sensor is interrupted On power on the sensor will always time an initial autocalibration interval first then settle into the regular autocalibration cycle The regular autocalibration timer is reset automatically if the user calibrates the sensor using the U G X F or u commands 6 4 Autocalibration Intervals The autocalibration intervals are set using the command This command allows the autocalibration periods to be set interrogated or disabled To set the autocalibration intervals the command structure is initialinterval regularinterval r n Where both the initial interval and regular interval are given in days Both must be entered with a decimal point and one figure after the decimal point For example send 1 0 8 0 r n response 1 0 8 0 r n Will set the autocalibration interval to 8 days and the initial interval to 1 day Note that there is a space between the and the first number and a space between the two numbers In hex the example above reads 40 20 31 2E 30 20 38 2E 30 OD OA 6 5 Readthe Autocalibration Settings To determine the current autocalibration settings send r n response 1 0 8 0 r n If the autocalibration is enabled the sensor will respond with the format above showing the initi
3. RR RN A ERR KC e EARN OEE RR ER FRA Era 10 5 1 Zero in a known gas concentration recommended essere 10 5 2 ZEFO IM Nitrogen UI M EA 11 5 3 Zero in Fresh Air assumed to be 400 Ppm ccccccccssceseessececeesseceeeeseeeecseaeeeeeeaeeeseesaeeeeeees 11 5 4 Fine Tune the Zero POIlnt osr eie rene ern Qoi ne repr antes Rx o ee nr e Qo i pre due agn 11 5 5 Zero Point AdjUstimient rrr Bored rex eg vien Rosen ege onines oaa d 12 6 A toCalibratiOn cerei T itera EUER TY ee Dura ROS RE RR eu ee Rau ERE Fea po a ya on ra dnte a UNE Neo 12 6 1 Principlef OperatiOh irri eoe renti ores eE ar e rae ea pre eR ue eost eue 12 6 2 Requirements for Auto calibration esses nennen nnn nennen nnns nenne nian 13 6 3 Setting the Auto Calibration Parameters esses ennemis 13 6 4 Autocalibration Intervals seeesss esses enne enne enne nnn ener ener nnne 14 6 5 Read the Autocalibration Settings eise eene nennen enne 14 6 6 Disable Autocalibration eese eene enne nnne nnns enne nnne sterne 14 6 7 Background Concentration cte ce Dette ie Dese aded Dei Uere e Dep ya dee 15 7 Altitude Compensation iiec cet rita erar eres irakere de aine a eae dene HERE e dE 15 8 User Settings EE 18 8 1 Digital Filter s src REC m 18 8 1 1 Customising the Sensor Response csessssccececseseseaecece
4. SST Sensing Ltd 5 www sstsensing com AN0114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY T r n where is a five digit number To convert to C subtract 1000 and divide by 10 For example T 01235 r n Represents 23 5 C NB The temperature and humidity sensor is a factory fit option If it is not fitted the sensor will return T 01000 1 3 8 Humidity Measurement Option The humidity measurement is reported as H r n Where is a five digit number To convert to relative humidity 96 divide by 10 For example H 00551 r n Represents 55 1 RH NB The temperature and humidity sensor is a factory fit option If it is not fitted the sensor will return H 00000 1 3 4 Example of T H and CO When shipped the sensor default output is CO only To output temperature humidity and CO send M 4164 r n see Output Fields The output format will have the form H 00345 T 01195 Z 00651 r n This example indicates 34 5 RH 19 5 C and 651ppm CO 2013 SST Sensing Ltd 6 www sstsensing com ANO114 rev4 Please follow all safety information 2 Command Summary SWITCHING SENSING TECHNOLOGY For complete details of the commands and their correct usage please refer to the Command Reference Command Use Example Response Comments A r n Set the digital Filter A16 r
5. character followed by a SPACE followed by a zero terminated by OxOd 0x0a CR amp LF Response o r n COMMAND 0x40 CALIBRATION USE WITH CAR Example 1 0 8 0 r n Description Set the Autocalibration timing Syntax See Autocalibration section Response 1 0 8 0 r n the number mirrors the input value 9 5 Polling Commands H COMMAND 0x48 INFORMATIO Example H r n Description Reports the humidity measurement from the temperature and humidity sensor if fitted Divide by 10 to get the RH Syntax ASCII Character H terminated by 0x0d Ox0a CR amp LF Response H 00551 r n T COMMAND 0x54 INFORMATIO Example T r n Description Reports the humidity measurement from the temperature and humidity sensor if fitted Subtract 1000 and divide by 10 to get the temperature in C Syntax ASCII Character T terminated by 0x0d 0x0a CR amp LF Response T 01224 r n Z COMMAND 0x5A INFORMATIO Example Z r n Description Reports the latest CO2 measurement in ppm Syntax ASCII Character Z terminated by 0x0d 0x0a CR amp LF Response Z 00512 r n 2013 SST Sensing Ltd 26 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Q COMMAND 0x51 INFORMATIO Example Qirin Description Reports the latest measurement fields as defined by the most recent M command Syntax ASCII Character Q terminated by 0x0d 0x0
6. conditions This is useful if there is a combination of steady state conditions with some periods of rapidly changing concentrations 8 13 Reading the Digital Filter Setting The current setting for the digital filter can be determined by sending a Vr in send a r n response a 00032 r n 8 2 User Options EEPROM Settings Some user settings can be altered in the internal EEPROM These settings can be set by using the parameter setting command P and read using a lower case aan p There are also 32 bytes of user EEPROM storage available 2013 SST Sensing Ltd 19 www sstsensing com ANO0114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY 8 2 1 Setting EEPROM To set an EEPROM location send P r n where the first parameter is the address and the second is the value Note that two byte values must be set one byte at a time For example to change the default value of the ambient gas concentration used for ambient calibration ie the assumed CO concentration in fresh air to 380ppm send send P 10 1 r n response P 00010 00001 r n send P 11 124 r n response P 00011 00124 r n 8 2 2 Reading EEPROM To read a parameter value from an EEPROM location send p r n where tt is the address of the parameter Note that two byte values must be read one byte at a time For example to read the value of the ambient gas concentration used for ambient calibration ie the ass
7. n A 00016 r n See User Settings a r n Return the digital a r n a 00016 r n See User Settings filter setting F HH HHH r n Fine Tune the zero F 410 400 r n_ F33000 r n See Zero Point Calibration point G r n Zero point G r n G 33000 r n See Zero Point Calibration calibration using fresh air H r n Return most recent H r n H 00552 r n 55 2 in the example humidity Humidity sensing is a factory measurement fit option K r n Selects the K 1 r n K 00001 r n See Operating Modes operating mode M HHHH r n Sets the output M 6 r n M 00006 r n See Output Fields fields P HHH HH r n Sets a user P110 r n P 00001 00010 r n See User Settings configurable field in EEPROM p HH Reads a user p 10 r n p 00010 00001 r n See User Settings configurable field from EEPROM Q r n Return most recent Q r n See Command Reference fields S HHA r n Sets the span S 8192 r n S 08192 r n See Span Calibration calibration value s r n Return the span s r n s 08192 r n See Span Calibration calibration value T r n Return the most T r n T 01225 r n 22 5 C in the example recent temperature Temperature sensing is a measurement factory fit option U r n Zero point U r n U 33000 r n See Zero Point Calibration calibration using nitrogen u HHHH r n Manual setting of u 32997 r n u 32997 r n See Zero Point Calibration the zero point X HHHH r n Zero point setting X 2000 r n X 32997 r n
8. D N C 3V3 N C Rx N C Tx Zero N C Ambient 1 2 Serial Connection O 2013 SST Sensing Ltd 3 ANO0114 rev4 WWW sstsensing com Please follow all safety information SWITCHING SENSING TECHNOLOGY The Rx and Tx pins are normally high suitable for direct connection to a UART If the sensor is to be read by a true RS232 device eg a PC it is necessary to pass through a level converter to step up down the voltage and invert the signal Connection to the sensor is via a 10 way 0 1 pitch connector In practice only the first 4 pins are required GND 3V3 Rx and Tx so a 4 way connector can be used A starter kit is available to allow simple interfacing between the sensor and a PC Contact SST www sstsensing com for details File Control Setup Measure Analyze Utilities Help 4 29 PM fei Ee Oe Scope trace showing command sent to the sensor green and sensor response yellow Parameter Value Baud Rate 9600 Data Bits 8 Parity None Stop Bits 1 Format UART normally high Hardware Flow Control None Voltage Voh 3V Voltage Vih 3V 5V NB If you connect to the sensor using HyperTerminal you must select the box Send line ends with line feeds under ASCII setup When initially powered the sensor will immediately start to transmit readings see Mode 1 in Operating Modes 2013 SST Sensing Ltd 4 www sstsensing com ANO114 rev4 Please follow al
9. ST engineering for their correct interpretation and use Measurement field are indicated in bold For example to output the temperature humidity and CO2 measurements send M 4164 rn The output string will then be H 12345 T 12345 Z 00010 r n 5 Zero Point Calibration There are a several methods to calibrate the zero point of the sensor The recommended method is zero point calibration in a known gas see X command which will give the most accurate zero setting In all cases the best zero is obtained when the gas concentration is stable and the sensor is at a stabilized temperature 5 1 Zero in a known gas concentration recommended Place the sensor in a known gas concentration and allow time for the sensor temperature to stabilize and for the gas to be fully diffused into the sensor Send the command X r n O 2013 SST Sensing Ltd 10 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY The concentration must be in the same units as the sensor output see Reading Format The sensor will respond with an echo of the command and the new zero point For example to set the zero point in a CO2S A when the sensor is in a known gas concentration of 2000ppm send X 2000 r n response X 32950 r n 5 2 Zeroin Nitrogen Place the sensor in a gas containing no CO typically nitrogen and allow time for the sensor temperature to stabilize and for the gas to be fully di
10. See Zero Point Calibration using a known gas calibration Y r n Return firmware Y r n See Command Reference version and sensor for details serial number Z r n Return the most Z r n Z 01521 r n 1521ppm in the example recent CO2 measurement 2013 SST Sensing Ltd 7 www sstsensing com AN0114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Command Use Example Response Comments H H H4 Nn Autocalibration 1 0 8 0 r n 1 08 0 r n See Autocalibration for configuration details r n Return the A r n 00100 r n Multiply by 100 in the multiplier required example to convert the Z output to ppm r n Return r n See the Command configuration Reference for details information All communications are in ASCII and are terminated by carriage return line feed ASCII characters 13 and 10 This document uses the protocol n to indicate the carriage return line feed All responses from the sensor including measurements have a leading space ASCII character 32 The character represents an ASCII representation of a numeric character 0 9 Note that there is a space between the first letter and any parameter For example the X command reads X space 2000 carriage return line feed Note that all settings are stored in non volatile memory so the sensor only has to be configured once It should not be configured every time it is pow
11. a CR amp LF Response H 12345 T 12345 Z 00010 r n 2013 SST Sensing Ltd 27 www sstsensing com ANO114 rev4 Please follow all safety information
12. al and regular autocalibration intervals If the autocalibration is disabled the sensor will repond with send r n response O r n 6 6 Disable Autocalibration 2013 SST Sensing Ltd 14 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY To disable the autocalibration send O r n response O r n ie followed by a space followed by a zero terminated with OxOd Ox0a 6 7 Background Concentration The background concentration depends somewhat on the area the sensor is installed Typically a figure between 400ppm and 450ppm is used The factory default is 400ppm To set this send P 8 x r n P 9 y r n where x and y depend on the concentration you want to set Concentration x Y 380 1 124 400 1 144 425 1 169 450 1 194 This is stored as a two byte value the high byte being in location 8 and the low byte in location 9 The value represents the concentration To calculate other values x int concentration 256 y the remainder after dividing concentration 256 7 Altitude Compensation Important This feature was introduced in sensors manufactured after July 2013 using firmware version AL17 or higher The firmware version can be identified by sending the Y or command Altitude compensation applies a permanent correction to the sensor response so should only be used when it is known that the sensor will be operating a
13. centration Response X 33000 r n the number is variable S COMMAND 0x53 CALIBRATION USE WITH CAR Example S 8192 r n Description Set the Altitude Compensation value in EEPROM Syntax ASCII character S SPACE decimal terminated by 0x0d Ox0a CR amp LF Response S 8192 r n the number mirrors the input value s COMMAND 0x73 INFORMATIO Example s r n Description Reports the Altitude Compensation value in EEPROM See Altitude Compensation Syntax ASCII Character s terminated by 0x0d 0x0a CR amp LF Response s 8193 r n u COMMAND 0x75 USE ONLY WITH SST GUIDANC Example u 32767 r n Description Send a zero set point Syntax ASCII character u SPACE decimal terminated by 0x0d Ox0a CR amp LF Response u 32767 r n NB For advanced use only Contact SST before using this command There are three variants of the autocalibration configuration command COMMAND 0x40 INFORMATIO Example r n Description Return the autocalibration settings Syntax ASCII character terminated by 0x0d Ox0a CR amp LF Response 1 0 8 0 r n if autocalibration is enabled O r n if autocalibration is disabled 2013 SST Sensing Ltd 25 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY COMMAND 0x40 CALIBRATION USE WITH CAR Example O r n Description Switch off the autocalibration function Syntax ASCII
14. e p 10 r n Description Returns a user configurable parameter Syntax P SPACE followed by an up to 2 digit number terminated by OxOd 0x0a CR amp LF Response P 10 1 r n see User Settings for details 9 2 Information Y COMMAND 0x59 INFORMATIO Example Y r n Description the present version string for the firmware Syntax ASCII character Y terminated by 0x0d 0x0a CR amp LF Response Y Jan 30 2013 10 45 03 AL17 r n B 00233 00000 r n NB This command requires that the sensor has been stopped see K command COMMAND 0x59 INFORMATIO Example r n Description Returns a number of fields of information giving information about the sensor configuration and behavior Syntax ASCII character terminated by OxOd 0x0a CR amp LF Response Contact SST for details COMMAND 0x2E INFORMATIO Example Arn O 2013 SST Sensing Ltd 23 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Description Returns a number indicating what multiplier must be applied to the Z or z output to convert it into ppm Syntax ASCII character terminated by 0x0d 0x0a CR amp LF Response 00001 r r this number is variable 9 3 Switching between Modes For discussion of different modes of operation see the section Operating Modes K COMMAND 0x4B USER CONFIGURATION Example K1 Description Switches the sensor between the o
15. ected reading Both parameters must be in the same units as the sensor output see Reading Format 2013 SST Sensing Ltd 11 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY The sensor will respond with an echo of the command and the new zero point For example send F 400 380 r n response F 32950 r n In this example the sensor zero point would be corrected so that a reading of 400ppm would now be reported as 380ppm 5 5 Zero Point Adjustment The precise zero point can be fine tuned by sending a zero point to the sensor This is not recommended for general use Send the command u r n where is the new zero point 6 AutoCalibration 6 1 Principle of Operation All CO sensors are fully calibrated prior to shipping from the factory Over time the zero point of the sensor needs to be calibrated to maintain the long term stability of the sensor In many applications this can happen automatically using the built in auto calibration function This technique can be used in situations in which sensors will be exposed to typical background levels 400 450ppm at least once during the auto calibration period For example many buildings will drop quickly to background CO levels when unoccupied overnight or at weekends The auto calibration function uses the information gathered at these periods to recalibrate O 2013 SST Sensing Ltd 12 www sstsensing co
16. ed SST Sensing Ltd will not accept any claim for damages howsoever arising as a result of use or failure of this information Your statutory rights are not affected This information is not intended for use in any medical appliance device or system in which the failure of the product might reasonably be expected to result in personal injury This document provides preliminary information that may be subject to change without notice The information in this guide is for the use of employees and customers of SST Sensing Ltd only This guide applies to software versions from July 2013 For previous versions please refer to CO2 Sensor Software USER s Guide Rev F Conventions In this guide r n Is used to indicate carriage return line feed characters Ox0d 0xOa which are required at the end of each string sent to the sensor and are appended to all transmissions from the sensor Z 12345 r n Courier fixed pitch font is used to show commands sent to the sensor and transmissions received from the sensor 2013 SST Sensing Ltd 2 www sstsensing com ANO114 rev4 Please follow all safety information 1 Serial Format and Connection 1 1 Connection Communication to and from the CO sensor is via a serial connection Pins are shown looking at the connector of the sensor SWITCHING SENSING TECHNOLOGY CO2S A GND N C 3V3 N C Rx N C Tx Zero N C Ambient CO2S W CO2F W GN
17. ered up 3 Operating Modes All CO sensors can be operated in three different modes Users can switch between the modes using the K command 3 1 Mode 0 Command Mode This is primarily intended for use when extracting larger chunks of information from the sensor for example using the Y and commands In this mode the sensor is stopped waiting for commands No measurements are made and the sensor will run through a warm up cycle after exiting this command There is no latency in command responses The power consumption is less than 3 5mW as no measurement activity takes place Commands which report measurements or alter the zero point setting are disabled in mode O Mode 0 is NOT retained after power cycling The sensor will always power up in streaming or polling mode whichever was the most recently used 2013 SST Sensing Ltd 8 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY 3 2 Mode1 Streaming Mode This is the factory default Measurements are reported twice per second Commands are processed when received except during measurement activity so there may be a time delay of up to 100mS in responding to commands The power consumption is 3 5mW assuming one field of information is transmitted and there is no temperature and humidity sensor 3 3 Mode2 Polling Mode In polling mode the sensor only reports readings when requested The measurement cycle continues
18. escesseseaeseeeeeseeseasaeeeeeesseesees 18 8 1 2 Setting the Digital Filter uei er onere dere cene u aree de c eese ERE RR 19 8 1 3 Reading the Digital Filter Setting cccccccccssssssssececececessessaeceecesesssesseaeeeeeesesssesenaeess 19 8 2 User Options EEPROM Settings cssssssssssssssssssssssssssssseseseeeeeeeseeeeeseeeeeaeseseaeeeaeaeaeaeees 19 8 2 1 Setting EEPROM ic LT Mm 20 2013 SST Sensing Ltd 1 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY 8 2 2 Wz nrddqcum E 20 8 2 3 EEPROM SEttiNg cm C aR 20 8 2 4 Autocalibration Settings locations 3 7 c ccccccsscccessssceceesssceceessececeesseeeceeaeeeeeeseeeeeees 21 8 2 5 User EEPROM mc 21 9 Command Reference ccssssccesccceiescecevessaiecsiagcicevesccdcesessguceva sia cedasaancesbasatccedadincesesvincdccdabincesdavandes 22 9 1 SUI E 22 9 2 IMPOR MATION ERREUR m 23 9 3 Switching between MOdE cssssccccccecsssessaececececeesesneaecesececesseseeaeseeeescesseaeaeeeesesseesesnaaeess 24 9 4 Zeroing and Calibration eter e eoi evene eee hen eee a Eaei 24 9 5 Polling Commands etcetera oontra ER e pun eee rE ea E ee den equ ERU ie 26 This documentation is provided on an as is basis and no warranty as to its suitability or accuracy for any particular purpose is either made or impli
19. ffused into the sensor Send the command U r n The sensor will respond with an echo of the command and the new zero point For example send U r n response U 32950 r n 5 3 Zero in Fresh Air assumed to be 400ppm If there is no calibration gas and no nitrogen available the sensor zero point can be set in fresh air The sensor is programmed to assume that fresh air is 400ppm this value is user configurable see User Settings Place the sensor in a fresh air environment and allow time for the sensor temperature to stabilize and for the fresh air to be fully diffused into the sensor Send the command G r n The sensor will respond with an echo of the command and the new zero point For example send G r n response G 32950 r n 5 4 Fine Tune the Zero Point If the CO2 concentration and the sensor reported concentration are known the zero point can be adjusted using the known concentration to fine tune the zero point This is similar in operation to the X command see above but can operate on historic data For example if the sensor has been in an environment in which it is know to have been exposed to outside air and the sensor reading is known at that time the zero point can be fine tuned to correct the reading This is typically used to implement automated calibration routines The command takes two parameters separated by a space The first parameter is the reading reported by the sensor The second is the corr
20. in the background but the output stream is suppressed The power consumption depends on the frequency of polling but is approximately the same as the streaming mode power consumption Note that the sensor will power up in the mode last used If it was last used in KO mode it will power up in either K1 or K2 mode depending on which was most recently used In Polling Mode measurements can be accessed using the polling commands H L Q T and Z see Command Reference 4 Output Fields The CO2S A and CO2S W sensors can be configured to output up to five fields of information Typically the only fields of interest are the CO concentration Temperature if fitted and Humidity if fitted This allows users to customise the output string transmitted by the sensor Up to five values can be transmitted in the string The format is always the same each field is identified by a single character followed by a space followed by the five digit number indicating the value of the parameter The output fields can be set by sending a command of the format M 12345 r n where 12345 represents a mask value which defines the output fields The mask value is created by adding the mask values for the parameters required see table below The sensor will output a maximum of five fields If the mask setting represents more than five fields only the first five those with the highest mask values will be output CO2F W sensors have a limited time to
21. l safety information SWITCHING SENSING TECHNOLOGY 1 3 Reading Format 1 3 1 CO Measurement The CO measurement is reported as Z z r n where Z shows the CO concentration after digitally filtering and z shows the instantaneous CO concentration without any digital filtering The concentration is reported in the following units Type Range Units Example CO2S PPM A Up to 296 ppm Z 00631 631ppm CO2S PPM W Up to 65 ppm 10 Z 01200 12000ppm 1 2 CO2S FR X W CO2S PPM W 100 Up to 100 ppm 100 Z 01500 150000ppm 15 CO2S FR X W 100 Note that the same units must be used when sending concentration information to the sensor for example the X command and the F command If in doubt the Command see below will indicate what multiplier should be applied to the Z output to convert to ppm Z 00842 z 00765 Sample output from a sensor with factory Z 00842 z 00738 settings Z 00842 z 00875 00858 This is a CO2S A so the reported CO reading is Z 0084 008tT 842ppm Z 0084 00839 2 2z 2z Z 00842 z 00817 2 amp 2 2 2 7 0084 00828 The second figure shows the instantaneous Z 0084 00850 unfiltered CO reading Z 0084 00875 See Digital Filter for more details Z 0084 00804 Z Z Zz Note that all output from the sensor has a leading space 1 3 2 Temperature Measurement Option The temperature measurement is reported as 2013
22. m ANO114 rev4 Please follow all safety information SST SWITCHING SENSING TECHNOLOGY 1000 900 800 700 600 500 400 300 200 100 0 CO2 Concentration ppm One Week gt This recording from a sensor shows a typical one week recording in an office environment The auto calibration function uses the low point circled and uses it to recalibrate the zero point 6 2 Requirements for Auto calibration Exposure to Fresh Air The sensor must see fresh air at least once during the auto calibration period You do not need to know when the fresh air will be sensed just that it will be sensed at some point during the period Continuously Powered The auto calibration information is deleted when the sensor is switched off This ensures that each installation is unaffected by any previous history of the sensor For auto calibration to function it must be power on for the whole of the auto calibration period 6 3 Setting the Auto Calibration Parameters Three parameters are required to enable the auto calibration routine Auto Calibration Interval This determines how often the auto calibration takes place Background Concentration Typically 400 450ppm This is the level the sensor will use as background Initial Auto calibration Interval It is possible for the first auto calibration to take place more quickly than the regular auto calibration event This can be useful to stabilize quickly after installation
23. me is in half second increments 13 BCLO Low byte of above 8 200 231 User EEPROM 255 8 2 4 Autocalibration Settings locations 3 7 These are included now to maintain compatibility with previous firmware versions SST recommends using the command to set autocalibration timings 8 2 5 User EEPROM Locations 200 to 231 can be used to store user values Each location is a single byte These locations are not used by the sensor Eg to store the number 42 in the first user EEPROM location send P 200 42 r n response P 00200 00042 r n and to read it send p 200 r n response p 00200 00042 r n Note that the EEPROM is only guaranteed for 100 000 write cycles 2013 SST Sensing Ltd 21 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY 9 Command Reference This gives the complete command set for the CO2S A CO2S W and CO2F W sensors and illustrates use of some of the more commonly used options Key points to note are e nall cases commands are terminated with a carriage return line feed rn e Commands are case sensitive e The commands use all use ASCII characters Each command lists the ASCII letter and includes the hex code for avoidance of doubt e Always check for a correct response before sending another command e fa command is unrecognized the sensor will respond with a WARNING This document is provided to give a com
24. mple to correct the sensor for permanent installation at 305m elevation send S 8494 r n response S 08494 r n Altitude ft Altitude m Barometric Pressure mbar Code 1000 305 1050 7889 0 0 1013 8192 1000 305 976 8495 2000 610 942 8774 3000 915 908 9052 4000 1219 875 9322 5000 1524 843 9585 The current setting can be determined by sending a lower case s send s r n response s 08494 r n 2013 SST Sensing Ltd 16 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY O 2013 SST Sensing Ltd 17 www sstsensing com ANO0114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY 8 UserSettings 8 1 Digital Filter 8 1 1 Customising the Sensor Response The CO measurement is passed through a digital filter to condition the signal The characteristics of the filter can be altered by the user to tune the sensor performance to specific applications The filter operates as a low pass filter increasing the filter parameter reduces measurement noise but slows the response There is a tradeoff between noise resolution and speed of response The filter can be set to a value between 1 and 65535 Settings larger than 64 are not recommended for normal use A low value will result in the fastest response to changes in gas concentration a high value will result in a slower response Note that the response is als
25. o determined by the diffusion rate into the sensor The default setting is 32 This chart shows the effect of changing the filter setting Sensor Noise vs Filter Setting Sensor Noise 1 2 4 8 16 32 64 Filter Setting Increasing the filter setting has a beneficial impact on noise so improves the sensor resolution It also slows the sensor response to transients This can be used to improve the detection of average CO conditions In building control for example a fast response to breathing near the sensor is undesirable If the transient response is important either for speed of response or because the shape of the transient is required a low filter setting should be used The following chart shows the same transient event capture using a filter setting of 4 and using a filter setting of 32 2013 SST Sensing Ltd 18 www sstsensing com ANO0114 rev4 Please follow all safety information SST SWITCHING SENSING TECHNOLOGY Effect of Filter on Transient Response 12000 10000 8000 Filter 4 6000 Filter 32 Reported CO2 4000 2000 8 1 2 Setting the Digital Filter To change the setting type A r n where is the required filter setting For most applications a filter setting of 32 is recommended send A 32 r n response A 00032 r n If the filter is set to zero a smart filter mode will be used in which the filter response is altered to suit the prevailing
26. perating modes Syntax ASCII character K SPACE followed by the mode number terminated by 0x0d 0x0a CR amp LF Response K 1 r n the number mirrors the input value 9 4 Zeroing and Calibration See examples of each of the zero and calibration commands in the following section U COMMAND 0x55 CALIBRATION USE WITH CAR Example U r n Description Calibrates the zero point assuming the sensor is in Oppm COs Syntax ASCII Character U terminated by 0x0d 0x0a CR amp LF Response U 32767 r n the number is variable G COMMAND 0x47 CALIBRATION USE WITH CAR Example G r n Description Calibrates the zero point assuming the sensor is in 400ppm CO Syntax ASCII character G Response G 33000 Nr An the number is variable F COMMAND 0x46 CALIBRATION USE WITH CARE Example F 410 390 r n Description Calibrates the zero point using a known reading and known CO concentration Syntax ASCII character F then a space then the reported gas concentration then a space then the actual gas concentration O 2013 SST Sensing Ltd 24 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Response F 33000 r n the numbers are variable X COMMAND 0x58 CALIBRATION USE WITH CAR Example X 1000 r n Description Calibrates the zero point with the sensor in a known concentration ofCO Syntax ASCII character X then a space then the gas con
27. plete reference of the command set and outputs from the CO2S A and CO2S W sensor It is intended for advanced users only If in doubt please contact SST engineering prior to use 9 1 Customisation A COMMAND 0x41 USER CONFIGURATION Example A 128 r n Description Set the value for the digital filter Syntax ASCII character A SPACE decimal terminated by 0x0d Ox0a CR amp LF Response A 00032 r n a COMMAND 0x61 INFORMATIO Example a r n Description Return the value for the digital filter Syntax ASCII Character a terminated by 0x0d 0x0a CR amp LF Response a 00032 r n M COMMAND 0x4D USER CONFIGURATION Example M 212 r n Description Determines which values are going to be returned by the unit Syntax M SPACE followed by an up to 5 digit number each bit of which dictates which item will be returned by the sensor terminated by OxOd 0x0a CR amp LF Response M 212 r n see Output Fields for details O 2013 SST Sensing Ltd 22 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY P COMMAND 0x50 USER CONFIGURATION Example P 10 1 r n Description Sets a user configurable parameter Syntax P SPACE followed by an up to 2 digit number SPACE followed by an up to 3 digit number terminated by OxOd Ox0a CR amp LF Response P 00001 00010 r n see User Settings for details p COMMAND 0x70 USER CONFIGURATION Exampl
28. t altitude permanently 2013 SST Sensing Ltd 15 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY NDIR gas sensors such as the CO2S A CO2S W and CO2F W family of sensors detect the concentration of gas by measuring the degree of light absorption by the gas analyte The degree of light absorption is then converted into a concentration reported by the sensor The absorption process is pressure dependant so that a change in pressure will cause a change in the reported gas concentration As the pressure increases the reported gas concentration also increases As the pressure decreases the reported concentration decreases This effect takes place at a molecular level as is common to all NDIR gas sensors In normal use the reading will vary by 0 196 of reading for each mbar change in barometric pressure the sensor are calibrated at 1013mbar If the sensor is installed at an elevated altitude the mean barometric pressure will be lower than 1013mbar It is possible to configure the sensor to correct for this effect by setting the altitude when installing This will apply a permanent correction to the output of the sensor depending on the altitude setting selected To apply this correction 1 Select the appropriate code from the table below intermediate values can be interpolated 2 Sendthe S r n to the sensor where is the code from the table below For exa
29. transmit information so no more than two fields should be selected for output Parameter Field Mask Comments Identifier Value 2013 SST Sensing Ltd 9 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY Humidity H 4096 Reports the humidity output of the Temperature and Humidity Sensor if Fitted D digitally filtered d 2048 Reports a value related to the normalized LED signal strength smoothed D unfiltered D 1024 Reports a value related to the normalized LED signal strength Zero Set Point h 256 Reports a value related to the normalized LED signal strength Sensor Temperature V 128 Reports a value which varies inversely with the sensor unfiltered temperature Temperature T 64 Reports the temperature output of the Temperature and Humidity Sensor if Fitted LED Signal digitally o 32 Reports a value which gives an indication of the LED signal filtered strength smoothed LED Signal unfiltered O 16 Reports a value which gives an indication of the LED signal strength Sensor Temperature V 8 Reports a value which varies inversely with the sensor filtered temperature smoothed CO2 Output Digitally Z 4 Digitally filtered CO2 reading Filtered CO2 Output not z 2 Instantaneous CO2 reading filtered Note that most fields are for advanced use only and require specific guidance from S
30. umed CO concentration in fresh air send p 10 r n response p 00010 00001 r n send p 11 r n response p 00011 00124 r n 8 2 3 EEPROM Settings Most of the EEPROM settings are two byte values indicated by HI and LO in the variable name in the following table We recommend contacting SST before altering the default values Location Name Purpose Default Value 0 AHHI Reserved 0 1 ANLO Reserved 0 2 ANSOURCE Reserved 0 3 ACINITHI Autocalibration Preload This preloads the 87 autocalibration timer so that the first autocalibration O 2013 SST Sensing Ltd 20 www sstsensing com ANO114 rev4 Please follow all safety information SWITCHING SENSING TECHNOLOGY occurs after a shorter time 4 ACINITLO Low byte of above 192 5 ACHI Autocalibration Interval Sets the time interval 94 between autocalibrations 6 ACLO Low byte of above 128 7 ACONOFF Switches Autocalibration ON OFF 0 8 ACPPMHI Autocalibration Background Concentration This 1 determines what background CO level is assumed for autocalibration 9 ACPPMLO Low byte of above 194 10 AMBHI Ambient Concentration for G command This 1 determines what background CO level is assumed for ambient calibration using the G command 11 AMBLO Low byte of above 194 12 BCHI Buffer clear time This will clear any incomplete 0 commands from the serial buffer after a fixed period of inactivity The ti
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