Detcon DM-634 User Manual

Page 17

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 con-

ditions 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 pre-amp 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 3.5.5-f for details on changing the RS-485 ID number.

The following section explains the details of the Modbus™ protocol that the DM-634 MicroSafe™ sensor supports.

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

ing 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% LEL, 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 Setpoint

This is the trip point for the f irst alarm.

High Byte

Low Byte

40004

Alarm 2 Setpoint

This is the trip point for the second alarm.

High Byte

Low Byte

40005

Status Bits

High Byte

Bit 7

Not used, always 0

Bit 6

Not used, always 0

Bit 5

Not used, always 0

Bit 4

Not used, always 0

Detcon Model DM-634 Oxygen Sensor PG.17