Detcon TP-624C - Manual (Page 20)

“System Fault”, “Zero Fault”, and “Range Fault” will also cause the mA output to drop to zero (0) mA until the
condition is corrected.
Sensor Life
The sensor life feature is a reference based on signal output from the sensor cell. When a sensor life of 25% or less
remains, the sensor cell should be replaced within a reasonable maintenance schedule.
3.11 RS-485 P
ROTOCOL
Model TP-624C MicroSafe™ 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 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 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 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 3.5.4-f for details on changing the RS-485 ID number.
The following section explains the details of the Modbus™ protocol that the TP-624C 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.
Register # 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
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 Alarm 1 Setpoint
This is the trip point for the f irst alarm.
Register # High Byte Low Byte
40004 Alarm 2 Setpoint
Detcon Model TP-624C Hydrogen Sulfide Sensor PG.20