Detcon FP-624C - Manual (Page 21)

Fail-Safe/Fault Supervision
Model FP-624C MicroSafe™ sensors are programmed for fail-safe operation. Any of the following fault condition
will activate the fault relay, illuminate the fault LED, and cause the display to read its corresponding fault condi-
tion: “SENSOR FAULT”, “SIGNAL FAULT”, “HEATER FAULT”, or “CAL FAULT”. A “Sensor Fault”,
“Signal Fault”, and “Heater Fault”, will also cause the mA output to drop to zero (0) mA.
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.
3.12 RS-485 P
ROTOCOL
Detcon 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 conditions
would make it impractical to place so many devices on the same pair of wires. If a multi-point system is being uti-
lized, 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 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
Model FP-624C Combustible Gas Sensor PG.21