TQ Environmental LTD
Product Manual TQ 4000
Filename: 7970H8 Page 17 of 27
3. Initial Setting Up Of Flammable Sensor Cards
On flammable sensors there is a requirement to set the zero on the electronic zero
on the associated flammable sensor card.
This is only required to be done once at installation, after installation any drift can
be compensated by the zero procedure in set up.
Refer to drawing 7970X, 7970V.
Connect up the flammable gas sensor as shown, open the front panel to give
access to the flammable gas sensor card.
3.1. Setting the Flammable Gas Sensor Head Voltage
With DVM set to a low range measure the voltage across VB and 0V at the
control unit. (This is factory set to approximately 2.07 - 2.1V record this
reading (V1).
Measure the flammable gas sensor head Voltage at the sensor head
between the blue and brown wire on DVM with the same range (V2) at the
sensor head
Subtract V1 - V2 = cable voltage loss.
Measure across VB and 0V at the control unit on the DVM and turn the
sensor Volts pot to a level equal to V1 + cable voltage loss.
3.2. Setting the Sensor Zero
With DVM on dc and most sensitive range connect negative probe to B sig
and positive probe to TP1. TP1 is a long leg left on a resistor. Adjust the
zero adjust pot to give +1.00mV (milliVolts) on the DVM. It is important that
the reading is +ve. Hence the reading can be set anywhere between +1.0
mV and 0mV. It is important the probes are the correct way around.
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