Detcon PI-600 User Manual

Page 33

NOTE 1: If the gas symbol has more than 6 characters, the symbol can be replaced by an abbreviated version of the

target gas name such as TOL or TOLUEN for Toluene which has a the symbol C6H5CH3. For epichlorohydrin (sym-

bol C3H5OCL) you can substitute the name EPI or EPICHL etc.

NOTE 2: When the Universal Transmitter is re-initialized and a new gas and range is entered, the previous customer

settings for span gas value, response factor, and zero offset are reset to default levels. This must be re-programmed back

to the customer specif ic settings.

3.14 RS-485 P

ROTOCOL

Detcon MicroSafe™ toxic gas sensors feature Modbus™ compatible communications protocol and are addressable via

rotary dip switches for multi-point communications. Other protocols are available. Contact the Detcon factory for spe-

cific 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 differ-

ent 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.

In most instances, RS-485 ID numbers are factory set or set during installation before commissioning. If required, the

RS-485 ID number can be set via rotary dip switches located on the preamp circuit board. However, any change to the

RS-485 ID number would require the sensor housing to be opened, thus declassif ication of the area would be required.

See section 3.2.5.4-f for details on changing the RS-485 ID number.

The following section explains the details of the Modbus™ protocol that the MicroSafe™ sensor supports.

Code 03 - Read Holding Registers, is the only code supported by the transmitter. Each transmitter contains 6 holding

registers which ref lect its current status.

High Byte

Low Byte

40000

Gas type

Sensor Life

Gas type is one of the following:

01=CO, 02=H2S, 03=SO2, 04=H2, 05=HCN, 06=CL2, 07=NO2, 08=NO, 09=HCL, 10=NH3, 11=LEL, 12=O2

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

Example: 85=85% sensor life

High Byte

Low Byte

40001

Detectable Range

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

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.

High Byte

Low Byte

40003

Alarm 1 Set point

This is the trip point for the f irst alarm.

High Byte

Low Byte

PI-600 Toxic Gas Sensors PG.33