Скачать или смотреть Murco Gas Detector (MGD) 2 Level System Bump Test & Calibration

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The following procedure is a bump test and calibration of an Murco Gas Detector (MGD) unit. This is a mains supply unit and caution should be applied when removing the Murco Gas Detector (MGD) cover.

The tools required are a digital volt metre with a resolution to 2 decimal places, crocodile clips and or a test probe, a flat bladed screw driver and a Murco Calibration Kit which includes your cylinder of calibration gas, flow regulator, flexible non- absorbent tubing and a vented calibration hood.

This is the Murco Gas Detector (MGD) unit. The Murco Gas Detector (MGD) has models for one or two levels of alarm and can range from 1 to 6 sensors connected to the controller. On the 1 level system the calibrations are carried out on the controller and on the 2 level systems the calibration is carried out on the sensor. For demonstration purposes we shall use a one channel unit for both the one and two level systems, using a semi-conductor sensor for halocarbon refrigerants such as R404.

For the 2 level systems, monitor the ground or zero volts at TP5 on the sensor PCB. The standby voltage output in clean air can be monitored at TP4 and can be adjusted using RV1. The low level alarm can be monitored at TP2 and adjusted by P8 and the high level alarm can be monitored at TP1 and adjusted by P7. The delays for the low and high level are fixed and cannot be removed but are approximately 25 seconds after reaching the alarm set point.

The electrical set up of the 2 level system is shown using the semi-conductor version for demonstration purposes. The rating label on the side of the MGD sensor gives you the standby voltage and alarm voltage factory set points. These values were established during the initial factory calibration of the unit. So with your volt metre between TP5 and TP4, check and record the voltage. If different to the label factory voltage then adjust RV1 to the standby voltage, normally zero point three volts, or as on the rating label, move the positive lead from TP5 to TP2 and adjust P8 for the low level as shown on the rating label. Then move the positive lead from TP2 to TP1 and adjust P7 for the high level as shown on the rating label.

The Bump Test:

There are two types of bump test -- the quantified bump test uses a known concentration of gas and the non quantified bump test uses an unknown concentration. For a 2 level system connect the volt metre between TP5 and TP4. Once the sensor starts to see gas this voltage should increase. For a quantified test you need to use a calibration cylinder for the target gas at a concentration as specified on the rating label or higher. Having carried out the electrical set up, expose the sensor to the gas here, you should see the standby voltage increase. It may take ten to fifteen minutes to pass the alarm set point. Older sensors may take longer. Once you've reached the alarm set point the low level yellow LED will come on and then the red LED will come on at a high level set point and the sounder if enabled will activate. The relays should also activate on the controller. The sounder can be muted by turning the key switch on the 2 level systems.

ON SCREEN TEXT: If a calibration cylinder is not available a non quantified bump test can be carried out using butane from a cigarette lighter. The set up for this test would be the same as the quantified bump test. Crack the valve open without igniting the gas.

The Calibration Process

There are two ways to carry out this calibration. One is to calibrate for the high level alarm and use electrical values to set the low level , this requires one cylinder of gas, and the other is to use two cylinders of target gas, one for each of the low level and the high level. For the purpose of this test we will use two cylinders of target gas.
Having carried out the electrical set-up and with the volt meter connected between TP5 and TP4 and with your known target gas and desired range, expose the sensor using the gas for the low level alarm and allow the standby voltage to climb. Once the voltage stops climbing and stabilises, record this voltage. Without removing the calibration hood from the sensor, change to the high level gas and allow the standby voltage to climb. Once the voltage stops climbing and stabilises, record this high level alarm voltage. For the first recorded voltage, monitor between TP5 and TP2 and adjust P8 to the recorded voltage. Then moving the positive lead from TP2 to TP1 adjust P7 to the higher alarm voltage and adjust P7 to approximately 50 milli-volts below the second recorded voltage. The MGD will now be in alarm and relays should activate. The sounder can be silenced by turning the key switch.

Remove the gas and the unit will come out of alarm and return to its normal voltage of 0.3 volts or as the settings on the rating label.