Det-Tronics MOS H2S Gas Sensor User Manual

Page 15

95-8532

1.4

Description

• When power is applied to the transmitter, it enters a Warmup mode to allow the sensor output to stabilize

before beginning normal operation. During this time the:

– Fault relay is de-energized.
– Alarm relays go to non-alarm state (either energized or non-energized, as programmed)
– Display alternates between “WARM-UP” and “MOS H

S.”

– Current output indicates a fault condition (less than 1.0 ma).

• The transmitter will stay in the Warmup mode for at least six seconds.
– If the detected gas at the end of the six second warmup period is higher than the lowest alarm setting or

if faults are present, the transmitter will remain in the Warmup mode until the detected gas falls below the

lowest alarm setting and no faults are present, or five minutes, whichever is shortest.

– If an alarm condition exists at the end of the five minute warmup, the transmitter will enter the Normal

operating mode and the alarm(s) will be annunciated.

– If a fault is present after the five minute warmup, the transmitter will indicate the fault, the fault relay will

remain de-energized, and the current output will be less than 1.0 ma.

• At the end of the warmup period with no faults or alarms present, the transmitter automatically enters the

Normal operating mode (fault relay energizes, alarm relays remain in non-alarm state), and the current

output will rise to 4.0 ma.

• I

n Normal operating mode with no alarm condition:

– Display is on and indicates the detected gas concentration.
– Alarm relays (on relay models) are in their normal state (energized or de-energized as programmed).
– 4 to 20 ma output signal level corresponds to the detected gas concentration.
– Fault relay (on relay models) is energized.

•

In the Normal operating mode with an alarm condition occurring:

– Display indicates the detected gas concentration.
– Low, Auxiliary or High display shows a black square, indicating alarm condition.
– Affected relay changes state (on relay models).
– 4 to 20 ma output signal level corresponds to the detected gas concentration.
– Fault relay output energized (on relay models).
– Relay History Indicator display shows an asterisk to indicate an alarm was activated.

•

When the signal decreases below setpoint:

– Display and 4 to 20 ma output continues to track the detected gas concentration.
– With latching operation programmed, no change to display indication or to alarm relay outputs.
– With non-latching operation programmed, low and/or Auxiliary display goes blank and Alarm relay

outputs return to their normal state. The High alarm will always latch.

– Asterisk in Alarm History Indicator display stays on to indicate an alarm since last reset.

•

In the event of a system fault:

– The normally energized Fault output is de-energized and the corresponding fault message is

displayed.

– 4 to 20 ma output drops to less than 1.0 ma.

•

In the event of an alarm condition and a system fault both occurring:

– In most cases, the first condition that occurs will be indicated by the current and relay outputs and on the

display.

– The exceptions are “CAL ABORTED” and “SENSOR E.O.L.” faults which both may occur during the

calibration procedure. If an alarm occurs with these faults, the alarm will over-ride the fault and will be

indicated.

Operating Mode

Warmup

Normal

Table 4—Infiniti Modes of Operation