SL-014 v1.6 Page29
Document Ref: SL-014 v1.6
This sequence first indicates
if the zero operation passed
or failed, then the new
detector reading then the
option to end and return to
the engineer menu. This
sequence effectively allows
the engineer to observe the
new detector zero point
before exiting.
Bottled Nitrogen or Instrument grade zero air
Regulator to deliver a
fixed flowrate (typically
between 0.5 to 1 L/min)
Hose delivers zero gas to the
detector. Note a test gas
applicator is usually required.
In some cases weather
protection guards or the
detector itself may include a
gas applicator port. If not the
correct calibration gas
adaptor must be used.
Gas Detector ZERO Function
All gas detectors will require periodic ZERO and CALIBRATION. The calibration interval depends on a number of
environmental factors such as: temperature variance, exposure to wind chill, rain, humidity changes and vibration
to list a few. As a guide line gas detectors should be checked at least yearly. As with any measuring instrument if
calibration is not held over the intervening interval then a shorter calibration interval may be required.
Detectors should always be zeroed first and then calibrated. Alarms should be isolated during this process. A
normal calibration sequence would consist of:
1. Assess zero reading in pre-zero condition and record by applying a zero gas typically Nitrogen or Instrument air
2. Assess calibration point by applying a known calibration gas. and record
3. If the zero and calibration points are /-2% of range then take no further action. zeroing and calibrating a
detector that already reads correctly will not improve its performance. If either is out then proceed to step 4.
4. Apply a suitable zero gas and zero the channel, observe and record result.
5. Apply a known calibration gas and calibrate the channel, observe and record the result.
Notes
Do not rely on the ambient environment to provide a zero point, Nitrogen or Instrument air should always be used
as appropriate. If there is a background level of the target gas and a zero is performed then the zero point will not
be correctly set.
To Zero the detector enter password mode
as previously described and enter
password 100 to enter the user menu.
Select menu item 1 ZERO
The top line of the display shows the
current reading. The bottom line shows the
current option.
With zero gas flowing and the reading stable
press the button to select CONTINUE. Now
press and hold the button until prompted to
release to action the zero request.
zero
1 of 10
8 PPM
Abort
0 PPM
Continue
ZERO
PASSED
0 PPM
CLICK TO
The display shows the result of the zero request, note that the actual zero and
calibration values are stored on the individual detector heads. When carrying out a
zero or calibration the controller sends the request to the detector head for action
and monitors the result. This means that detectors can be supplied pre-calibrated
The reading is now displayed so the result of the zero request can be observed.
The reading should be stable. Click the button to return to the previous menu.
Repeat the sequence if you are not /-2% of zero.
Calibration
Zero
Gas
Gas
20% LEL
