5 DETECTOR HEAD OPERATION & CALIBRATION
For details regarding FGD detector head specifications consult section 1.
5.1 Detector Head Variants
Status Scientific Controls manufacture detector heads for a wide variety of gases. The flexibility of
the MCU systems has led to alternative heads being designed to monitor alternative parameters
e.g. temperature (thermocouples), fire/smoke etc.
Status Scientific Controls can manufacture detector heads allowing the MCU system to monitor
almost any measurable level (not necessarily related to environmental monitoring). Contact
Status Scientific Controls for further details.
5.2 Operation
The FGD2 & FGD3 detector heads do not require user intervention during normal operation;
however periodic inspection is advised (consult section 5.3). The front panel LCD will always
show the current levels of gas that the head is detecting. A Confidence LED located on the lower
edge of the casing will flash periodically to indicate that the head is powered and the internal
microcontroller is running.
5.2.1 Status Indications
5.2.1.1 FLT
The flammable gas detector heads incorporating pellistors will flash ‘FLT’ if they sense a fault with
the pellistors fitted. This will coincide with them drawing less than 2.5mA from the control unit,
thus ensuring the control unit is aware of the fault condition.
All other detector heads will flash FLT if they sense a gas concentration less than 10% of FSD
below zero.
5.2.1.2 Calibration Mode
When the Detector head is placed in calibration mode, the display will flash the appropriate
information.
5.2.1.3 HI
HI will flash on the display if the head detects a gas concentration greater than:
FSD + 10%.
e.g. A flammable head with a range of 0-100% LEL
10% of full scale is 100/10 = 10%
If the reading goes above fsd by 10% (i.e. 110% LEL), HI will flash on the display.
This condition will coincide with the head drawing a current of greater than 22mA, thus indicating
to the MCU Control Unit of a HI condition.
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