MGS Installation and Operation Manual
20
1000-0085 Rev 0
Section 4. Operation and Stabilisation
On powering up, the MGS will sense for the presence of gas after an initial
warm-up delay of 5 minutes. The green LED will flash at 1 second intervals
during the warm-up.
In an alarm condition:
•
green LED stays on and the red LED is on
•
audible alarm operates (if not disabled and after delay, if set).
•
relay output activates (after a delay, if set)
•
V and I output changes proportionally with gas concentration.
In a fault condition:
•
green LED will be off and the red LED will be on
•
voltage/current fault output will activate:
o
2mA on the 4-20mA output
o
0.5V on the 1-5V output
o
1.0V on the 2-10V output.
The typical time for various sensor types to stabilise is shown below.
Sensor Type
Stabilisation Time
Electrochemical (EC)
20-30 seconds
Semiconductor (SC)
1-3 minutes
Infrared (IR)
2 minutes
On power up, the electrochemical sensor outputs a signal voltage normally
below the set alarm level. Semiconductors output over the + max scale, i.e.,
> 5V. Both move towards zero as they stabilise.
If sensors have been in long-term storage or the detectors have been turned
off for a long period, stabilisation is much slower. However, within 1-2 hours
sensors should have dropped below the alarm level and be operational. You
can monitor progress exactly by monitoring the 0-10V output. When the
output settles around zero the sensor is stabilised. In exceptional
circumstances the process can take up to 24 hours or more.