Detcon PI-700 0-500ppb - Manual (Page 29)

Model PI-700 0-500ppb
PI-700 0-500ppb Instruction Manual Rev. 0.0 Page 25 of 53
4. RS-485 Modbus™ Protocol
Model PI-700 sensors feature Modbus™ compatible communications protocol and are addressable via the
program mode. Other protocols are available. Contact the Detcon factory for specific protocol requirements.
Communication is two wire, half duplex 485, 9600 baud, 8 data bits, 1 stop bit, no parity, with the sensor set
up as a slave device. A master controller up to 4000 feet away can theoretically poll up to 256 different
sensors. This number may not be realistic in harsh environments where noise and/or wiring conditions would
make it impractical to place so many devices on the same pair of wires. If a multi-point system is being
utilized, each sensor should be set for a different address. Typical address settings are: 01, 02, 03, 04, 05, 06,
07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11…etc.
Sensor RS-485 ID numbers are factory default to 01. These can be changed in the field via the Operator
Interface described in Section 3.5.5 Set Serial ID.
The following section explains the details of the Modbus™ protocol that the PI-700 sensor supports.
Code 03 - Read Holding Registers, is the only code supported by the transmitter. Each transmitter contains 6
holding registers which reflect its current status.
Register #
High Byte Low Byte
40000 Gas type
Gas type is one of the following:
01=CO, 02=H
2
S, 03=SO
2
, 04=H
2
, 05=HCN, 06=CL
2
, 07=NO
2
, 08=NO, 09=HCL, 10=NH
3
, 11=LEL, 12=O
2
Register #
High Byte Low Byte
40001 Detectable Range
i.e. 100 for 0-100 ppm, 50 for 0-50% LEL, etc.
Register #
High Byte Low Byte
40002 Current Gas Reading
The current gas reading as a whole number. If the reading is displayed as 23.5 on the display, this register
would contain the number 235.
Register #
High Byte Low Byte
40003 Auto Span Level
Register #
High Byte Low Byte
40004 Sensor Life
Sensor life is an estimated remaining use of the sensor head, between 0% and 100%.
Example: 85=85% sensor life
Register #
High Byte Low Byte
40005 Status Bits Status Bits