CO2 TRANSDUCER CO2-SENS-D-MODRTU VTS reserves the right to implement changes without prior notice. www.vtsgroup.com Page 1 of 16 ver. 2.0 (11.
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 ▪ ▪ ▪ ▪ 1.2.
2. Technical data 2.1. General parameters of the transducer Power supply DC voltage DC 20-30 V (nom DC 24 V) AC voltage AC 20-28 V (nom AC 24 V) Current consumption typical max 30 mA 100 mA LED indicators See section 3.5 Signal connection Screw terminals in 5 mm pitch (wire diameter ≤ 2.
2.3. Parameters of analogue output Output type voltage Output range 0-5 V or 0-10 V Resolution 11.5 bit in [mV] for the range 0-10 V 3.2 mV~ in [mV] for the range 0-5 V 1.6 mV~ RL > 1 kΩ Loading capacity Refreshing period 1s 2.4.
3.2. Device design VTS reserves the right to implement changes without prior notice. www.vtsgroup.com Page 5 of 16 ver. 2.0 (11.
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.
3.4.
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. No. 1 Description Power supply present 3.5.2. No.
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).
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.
Command table: Command no.
4.1.1. Bit no. 15 14 name DEV_ID_REG (addr=11=0x000B) – read only 13 12 11 DEV[4..0] 10 9 8 HV[1..0] 7 6 5 4 OPTIONS[4..0] 3 2 1 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..
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 Size [Bytes] 1 1 1 2*N 2 Values 1 – 247 0x03 2* n Acc. to register map 0x0000 – 0xFFFF Size [Bytes] 1 1 1 2 Values 1 – 247 0x83 1– 4 0x0000 – 0xFFFF Notes See section 4.
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 Size [Bytes] 1 1 1 2 Values 1 – 247 0x86 1–4 0x0000 – 0xFFFF Notes See section 4.4 Error format: Description Address Function code Error code CRC check sum 4.2.3. Notes See section 4.2.4 See section 4.
Error format: Description Address Function code Error code CRC check sum 4.2.4. Size [Bytes] 1 1 1 2 Values 1 – 247 0x90 1–4 0x0000 – 0xFFFF See section 4.2.4 See section 4.4 Description of errors CODE 0x01 0x02 0x03 0x04 4.3. Notes Name Invalid function Invalid data range / address Invalid data value SLAVE device error Data format 4.3.1. Character / byte format The following figure shows the format of a byte transmitted in the MODBUS RTU protocol.
4.4.
