Detcon 1000 - Manual (Page 22)

Mdl 1000 H2S E-Chem / Inst. Air
Model 1000 H2S E-Chem w Instrument Air Rev. 1.1 Page 18 of 28
8. Programming Features
Detcon MicroSafe™ H
2
S gas sensors incorporate a comprehensive program to accommodate easy operator
interface and fail-safe operation. Program features are detailed in this section. Each sensor is factory tested,
programmed, and calibrated prior to shipment.
Over Range
When the sensor detects gas greater than 100% of its range, it will cause the display to flash the highest
reading of its range on and off.
Under Range Faults
If the sensor should drift below the zero baseline by approximately 10% of range, the display will indicate a
fault: “ZERO FAULT”. If the sensor drifts below the normal zero baseline by approximately -30% of range,
the display will indicate a “SIGNAL FAULT”.
Calibration Fault
If during calibration the sensor circuitry is unable to attain the proper adjustment for zero or span, the sensor
will enter into the calibration fault mode and cause the display to alternate between the sensor’s current status
reading and the calibration fault screen which appears as: “CAL FAULT”.
Fail-Safe/Fault Supervision
Detcon MicroSafe™ sensors are programmed for fail-safe operation. Either fault condition will activate the
fault relay, illuminate the fault LED, and cause the display to read its corresponding fault condition: “SIGNAL
FAULT”, or “CAL FAULT”. A “SIGNAL 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.
9. RS-485 Protocol
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 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
declassification 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 Detcon MicroSafe™ sensor
supports.