Manual

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.

40000 Gas type

Gas type is one of the following:

01=CO, 02=H

S, 03=SO

, 04=H

, 05=HCN, 06=CL

, 07=NO

, 08=NO, 09=HCL, 10=NH

, 11=LEL, 12=O

40001 Detectable Range

i.e. 100 for 0-100 ppm, 50 for 0-50% LEL, etc.

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.

40003 Auto Span Level

40004 Sensor Life

Sensor life is an estimated remaining use of the sensor head, between 0% and 100%.

Example: 85=85% sensor life

40005 Status Bits Status Bits