VTS Group - Air Handling and Conditioning units, Air Curtains, Heating UnitsVTS Group - Air Handling and Conditioning units, Air Curtains, Heating Units
Instruction Manual for VTS models including: CO2-SENS-D-MODRTU CO2 Concentration Transducer, CO2-SENS-D-MODRTU, CO2 Concentration Transducer, Concentration Transducer, Transducer
Compact Floor-Mounted Air Handling Units | Ventus - VTS Group
VTS Group ventilation systems
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DocumentDocumentCO2 TRANSDUCER CO2-SENS-D-MODRTU
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1. Introduction
This document describes functionality of CO2 concentration transducer based on integrated MH-Z19B sensor, equipped with RS-485 interface using MODBUS RTU protocol and 0-5V / 0-10V analogue output.
NOTES:
1) Read this document carefully before attempting to start up the device!
2) The device must be installed by qualified staff only.
1.1. Functions of the device
CO2 measurement 0-5V or 0-10V analogue output (hardware selectable range) proportional to
CO2 concentration 3 status LEDs RS485 serial interface for remote management (setup and reading of
measurement values) MODBUS RTU protocol integrated terminating resistor 120 communication in HALF DUPLEX mode hardware/software configurable address in the range 1-247 hardware configurable communication baud rate: 19200, 9600, 4800, 2400 software configurable communication baud rate: 115200, 57600, 38400, 19200, 9600, 4800, 2400
1.2. Device characteristics
The main function of the CO2 transmitter is to measure the CO2 concentration in the air using an integrated MH-Z19B sensor. The measurement result, as well as the sensor missing/error status, is processed by the built-in microprocessor and then made available on the RS-485 bus via registers of the MODBUS RTU protocol. Additionally, the measurement result is available as analog signal on the 0-5V / 010V voltage output.
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2. Technical data 2.1. General parameters of the transducer
Power supply
DC voltage AC voltage
Current consumption
typical max
LED indicators
Signal connection
Housing dimensions without sampling mast with sampling mast
Weight Working environment Working temperature
DC 20-30 V (nom DC 24 V) AC 20-28 V (nom AC 24 V)
30 mA 100 mA See section 3.5 Screw terminals in 5 mm pitch (wire diameter 2.5 mm)
80x82x55 mm 80x82x280 mm
230g Dust-free, air, neutral gases
0ºC ÷ 50ºC
2.2. Parameters of CO2 measurement
Sensor model
MH-Z19B
Measurement range
0/400-2000 ppm
Measurement accuracy
± (5% of measured value + 50ppm)
Sampling period
5 s
Response time T90 *)
< 2 min
*) response time T90 is the time from moment of change of state to the moment when the measurement value reaches 90% of the steady value.
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2.3. Parameters of analogue output
Output type Output range Resolution
in [mV] for the range 0-10 V in [mV] for the range 0-5 V Loading capacity Refreshing period
voltage 0-5 V or 0-10 V
11.5 bit 3.2 mV~ 1.6 mV~ RL > 1 k
1 s
2.4. Parameters of serial interface
Transmission interface
RS-485
Communication protocol
MODBUS RTU
Transmission type
HALF DUPLEX
Communication baud rate
2400 / 4800 / 9600 / 19200 / 38400 / 57600 / 115200 Baud/s
Integrated resistor terminating the RS-485 bus
120
3. Installation 3.1. Safety The device must be installed by qualified staff only! All connections must be made in accordance with wiring diagrams
shown in this document!
Check all electrical connections prior to commissioning!
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3.2. Device design
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3.3. Description of terminals
OR POWER SUPPLY
Notes: 1. The RXTX+ and RXTX- signals must be connected to the A and B lines of the MODBUS bus respectively. 2. The analogue output returns following voltage values:
Vout
VOLTAGE RANGE 2000 ppm
CO2CONCENTRATION
whereas the concentration value can be calculated basing on the voltage value form using the following formula:
CO 2CO NCE NTR A TIO N
2000 ppm VOLTAGE RANGE
VOUT
where: VOLTAGERANGE = 5V or 10V (0-5V or 0-10V set on the configuration DIP-switch 2 see section 3.4)
Exemplary values are shown in the table below:
CO2 concentration [ppm]
Voltage range = 5 V
0
0.0V
400
1.0V
1000
2.5V
2000
5.0V
Voltage range = 10V 0.0V 2.0V 5.0V 10.0V
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3.4. Configuration of MODBUS bus, serial port and analogue output
0 OFF
1 ON
CONFIGURATION
ADDRESS
The purpose of the consecutive switches of the left DIP-switch is as follows (default values are in bold)
1 2 3 4 5 6
ON OFF
ON OFF
ON ON ON OFF OFF ON OFF OFF
ON ON ON OFF OFF ON OFF OFF
Effect Terminating resistor 120R switched on Terminating resistor 120R switched off
Analogue output range 0-5V Analogue output range 0-10V Use BAUDRATE and PAR from the software configuration PAR - parity check (1 STOP bit) PAR - no parity check (2 STOP bits) PAR - no parity check (1 STOP bit)
BAUDRATE=2400 BAUDRATE=4800 BAUDRATE=9600 BAUDRATE=19200
The device address on the MODBUS bus is set using the right DIP-switch:
123 4 5 6 7 8
ON ON ON ON ON ON ON ON
Effect Address = address + 1 Address = address + 2 Address = address + 4 Address = address + 8 Address = address + 16 Address = address + 32 Address = address + 64 Address = address + 128
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Note: the configuration set by the means of DIP-switches is read once after device restart (after switching on the power or pressing the RESET button). For this reason, if the DIPswitch settings are changed during operation, then after changing the settings, it is necessary to restart the device by pressing the RESET button or temporarily unplugging the power supply.
3.5. LED indicators
3.5.1. LED POWER
No.
Description
1
Power supply present
Color / mode of light Red flashing 1000 ms / 1000 ms
3.5.2. LED LINK
No.
Description
1
Data transmission on the bus
2
No transmission
Color / mode of light Green continuous light / irregular flashing
LED off
3.5.3. LED SENSOR
No.
Description
1
Warm up of the CO2 module
2
0 799 ppm
3
800 1199 ppm
4
1200 1999 ppm
5
2000 ppm
6
Sensor missing or other error
Color / mode of light
Green flashing 250 ms / 250 ms Green continuous light Yellow continuous light Red continuous light
Red flashing 1000 ms / 1000 ms Red flashing 100 ms / 600 ms
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3.6. Recommendations for installation
TRANSDUCER (1)
TRANSDUCER (2)
TRANSDUCER (n)
It is recommended that devices on the MODBUS (RS485) are connected in a daisy-chain configuration, whereby 120R terminating resistors should be connected between A and B lines of the bus at both ends of the chain (close to the outer devices). This resistor is builtin in the CO2-SENS-D-MODBRTU transducer and can be switched on using the no. 1 switch on the configuration DIP-switch (see section 3.4).
Moreover, shielded cables should be used when the device is operated in high interference environments and the shield should be connected to the nearest PE point on the power supply side.
3.7. The automatic zero calibration (ABClogic function)
It is assumed that CO2 concentration in the outdoor air amounts to 400 500 ppm. The CO2 concentration inside buildings is higher, mainly due to the presence of people. When there are no people in the building and the ventilation systems works properly, the CO2 concentration inside the building decreases to a level close to those of outdoor air.
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ABClogic is an algorithm for long term tracking of CO2 concentration and adjusting the sensor characteristics in the low concentration range. The sensor stores low values of CO2 concentration from many last days, which enables taking intelligent account of periodical CO2 concentration level increases (e.g. when rooms were used 24 hours per day over a few days). As a result of the ABClogic algorithm, the "automatic zero calibration" of the sensor is carried out.
The automatic calibration ABClogic, is designed for applications where rooms remain unoccupied for several hours per day, as a result, CO2 concentration values periodically drop to low values, similar to those outside the building. In contrast, in an environment where the level of CO2 concentration reaches high values and doesn't drop to low values, the ABClogic system should be switched off, because it would adjust automatic calibration to the lowest levels, distorting the values indicated by the sensor.
In the sensor described in this document, the ABClogic function is off by default (factory setting). The status of ABClogic function (switching on or off) can be changed by writing the respective command (see section 4.1.1).
4. MODBUS protocol
4.1. Register map
Register R/W no.
0x0000 R 0x0001 R
0x0002 R
0x0003 RW 0x0004 RW 0x0005 RW
0x0006 R 0x0007 R 0x0008 R 0x0009 R 0x000A R 0x000B R 0x000C R
Name
VALUE_REG STATUS_REG
TEST_VAL_REG
PASS_REG COMMAND_REG
PARAM_REG
-----DEV_ID_REG SOFT_VER_REG
Values
Notes
0 - 2000 0 / 1 / 2 / 3
1000 (0x3E8)
CO2 concentration in [ppm]
0-Sensor missing, 1 correct operation, 2 sensor error, 3 warm up (first 3 minutes
after start)
Test value to verify the correctness of register readings
1234 (0x04D2) 1 / 2 / 3 / 4 / 5 / 6 Refer to command
table 0 0 0 0 0
0xC100 0 0x9999
password register command register parameter register
reserved reserved reserved reserved reserved Device identification Software version (e.g. 0x3210 means software 3.21a)
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Command table:
Command no. 1 2
Function Set device address Set the baud rate
3
4 5 6 Notes:
Set parity bits
Set stop bits Function on / off
Device reset
Parameters
1-247 (1 default value)
24 2400 bit/s 48 4800 bit/s 96 9600 bit/s 192 19200 bit/s = default value 384 38400 bit/s 576 57600 bit/s 1152 115200 bit/s
0 NO PARITY, no parity bit (default value) 1 EVEN PARITY 2 ODD PARITY
1 1x STOP, 1 stop bit (default value) 2 2x STOP, 2 stop bits
0 ABClogic off (off by default) 1 ABClogic on
1 software reset of the device 2 software reset of sensor module
Reading registers from addresses not listed in this table results in 0x02 exception.
Specifying an incorrect or out-of-range parameter value results in entering the value 0xEEEE into the command register.
The device is configured by writing three registers (password / command / parameter) at the same time using the 0x10 function with the corresponding values according to the command table, or by writing single registers (using 0x06 or 0x10 function) with the latter writing of a (valid) password causing the execution of the command.
During a single password entry (both with function 0x06 and 0x10) in case of a password match, the correctness of information in command and parameter registers is checked and if correct, the command is executed.
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4.1.1. DEV_ID_REG (addr=11=0x000B) read only
Bit no. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
name
DEV[4..0]
HV[1..0]
OPTIONS[4..0]
0 0 T[1..0]
This register is used to store device ID. Meaning of bits:
DEV[4..0] = b11000 fixed value meaning "air parameter sensors" HV[1..0] value 0..3 hardware version OPTIONS[4..0] values 0..31 device type
b10000 CO2 transducer with MH-Z19B sensor T[1..0] value 0..3 type
0 duct type 1 room type 2, 3 - reserved
CO2 duct sensor in basic hardware version returns the value b1100000100000000=0xC100.
4.1.2. SOFT_VER_REG (addr=12=0x000C) read only
Bit no. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
name
N[3..0]
A[3..0]
B[3..0]
REV[3..0]
Software version is represented as a sting of 4 characters: N.ABrev where N, A, B are digits in the the 0..9 range rev (with values 0..9) is a letter in the range `a'...'j'. Examples: 0x0000 represents software version: 0.00a; 0x4321 4.32b ; 0x2345 2.34f
4.2. Protocol functions
CODE 0x03 (dec 3) 0x06 (dec 6) 0x10 (dec 16)
Name Reading N x 16-bit registers Writing single 16-bit registers Writing N x 16-bit registers
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4.2.1. Reading the contents of a group of output registers (0x03)
Command format:
Description Address
Function code Data block address Number of registers (N)
CRC check sum
Size [Bytes] 1 1 2 2 2
Values
1 247 0x03
0x0000 0xFFFF 1 125
0x0000 0xFFFF
Notes See section 4.4
Response format:
Description Address
Function code Byte counter Register values CRC check sum
Size [Bytes] 1 1 1
2 * N 2
Values 1 247 0x03
2* n Acc. to register map
0x0000 0xFFFF
Notes See section 4.4
Error format:
Description Address
Function code Error code
CRC check sum
Size [Bytes] 1 1 1 2
Values 1 247 0x83
1 4 0x0000 0xFFFF
Notes
See section 4.2.4 See section 4.4
4.2.2. Writing single 16-bit registers (0x06)
Command format:
Description Address
Function code Register address Value to be stored CRC check sum
Size [Bytes] 1 1 2 2 2
Values
1 247 0x06
0x0000 0xFFFF 0x0000 0xFFFF 0x0000 0xFFFF
Notes See section 4.4
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Response format:
Description Address
Function code Register address Value to be stored CRC check sum
Size [Bytes] 1 1 2 2 2
Values
1 247 0x06
0x0000 0xFFFF 0x0000 0xFFFF 0x0000 0xFFFF
Notes See section 4.4
Error format:
Description Address
Function code Error code
CRC check sum
Size [Bytes] 1 1 1 2
Values 1 247 0x86 1 4 0x0000 0xFFFF
Notes
See section 4.2.4 See section 4.4
4.2.3. Writing a group of output registers (0x10)
Command format:
Description Address
Function code Data block address Number of registers (N)
Byte counter Values to be stored
CRC check sum
Size [Bytes] 1 1 2 2 1
2 * N 2
Values 1 247 0x10 0x0000 0xFFFF 1 123 2 * N 0x0000 0xFFFF 0x0000 0xFFFF
Notes See section 4.4
Response format:
Description Address
Function code Data block address Number of registers (N)
CRC check sum
Size [Bytes] 1 1 2 2 2
Values
1 247 0x10
0x0000 0xFFFF 1 123
0x0000 0xFFFF
Notes See section 4.4
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Error format:
Description Address
Function code Error code
CRC check sum
Size [Bytes] 1 1 1 2
Values 1 247 0x90 1 4 0x0000 0xFFFF
Notes
See section 4.2.4 See section 4.4
4.2.4.
CODE 0x01 0x02 0x03 0x04
Description of errors
Name Invalid function Invalid data range / address Invalid data value SLAVE device error
4.3. Data format
4.3.1. Character / byte format
The following figure shows the format of a byte transmitted in the MODBUS RTU protocol. Each transmitted character has 10 or 11 bits, which are sent in order from the least significant to the most significant.
With even / odd parity check START 1 2 3 4 5 6 7 8 PAR STOP Without parity check (1 or 2 stop bits): START 1 2 3 4 5 6 7 8 STOP (STOP)
4.3.2. Order of bytes in 16-bit data fields in a transmission frame
The following figure shows the byte order of the 16-bit data fields. For 16-bit data fields, the correct byte order is that the older byte is transmitted first, then the younger byte (HILO - BIG ENDIAN), while for the CRC field the younger byte is transmitted first, then the older byte (LO HI - LITTLE ENDIAN).
REG-0 (16bit)
HI
LO
DATA
REG-1 (16 bit)
REG-N (16bit)
...
HI
LO
HI
LO
CHECK SUM
CRC (16bit)
LO
HI
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4.4. CRC check sum
WORD CRC16 (const BYTE *nData, WORD wLength) { static const WORD wCRCTable[] = { 0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241, 0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440, 0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40, 0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841, 0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40, 0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41, 0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641, 0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040, 0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240, 0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441, 0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41, 0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840, 0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41, 0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40, 0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640, 0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041, 0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240, 0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441, 0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41, 0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840, 0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41, 0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40, 0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640, 0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041, 0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241, 0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440, 0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40, 0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841, 0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40, 0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41, 0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641, 0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040};
BYTE nTemp; WORD wCRCWord = 0xFFFF;
while (wLength--) {
nTemp = *nData++ ^ wCRCWord; wCRCWord >>= 8; wCRCWord ^= wCRCTable[nTemp]; } return wCRCWord;
}
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