45
WARNING
Prior to carrying out any work ensure local regulations and
site procedures are followed. Never attempt to open the
detector or junction box when flammable gas is present.
Ensure that the associated control panel is inhibited so as to
prevent false alarms.
3.1
Commissioning procedure
1. Open the junction box of the detector by unscrewing the lid in an anti
clockwise direction (having loosened the retaining grubscrew first).
2. Check that all electrical connections have been made and are correct,
as shown in Diagram 13.
3. Measure the voltage across the ‘+’ and ‘’ terminals and check a
minimum supply of 10 V dc. is present.
4. Leave the detector to stabilise for at least 1 hour.
5. Before calibration of the detector can commence, the pellistors must
be balanced. To do this remove the PCB cover, and connect a digital
volt meter (DVM) to the test points marked ‘TP3’ and ‘TP4’ on the
amplifier PCB, as shown in Diagram 12). The DVM should be set to the
dc mV range, and the potentiometer marked ‘VR3’ should be adjusted
until the DVM reads 0.00 mV. The PCB cover can now be replaced.
6. To zero the detector, reconnect the DVM to the test points marked
‘TP1’ and ‘TP2’ on the amplifier PCB, as shown in Diagram 12.
Note: At the test points, Zero will read 40 mV = 4 mA.
Full scale deflection (100% LEL) will read 200 mV = 20 mA. There is a
current clamp of 25 mA on the 420 mA output.
Zeroing the detector
7.
Ensure you are in clean air
. Adjust the ‘ZERO’ pot on the amplifier
(which is accessible via a hole in the PCB cover) until the DVM reads
40 mV. Check that the control equipment display reads zero.
Calibrating the detector
8. Apply calibration gas (concentration should be 50% LEL) to the
detector at a flow rate of 0.5 1 litre/minute via a flow adaptor (
Part
No. C03005
). Contact Crowcon for the supply of calibration gas.
9. Allow the gas reading to stabilise (usually 30 to 60 seconds) and adjust
the ‘CAL’ pot until the DVM reads the appropriate reading (ie 120 mV
= 12 mA = 50% LEL). If the concentration of the calibration gas used
is not 50% LEL, the following formula can be used to calculate the
reading:
3. Operation
Xgard Type 5