Retrotec DM-2 - Manual (Page 37)

Page 37 of 72
©Retrotec Inc. 2012
If the readings are different, either one tube is blocked or the gauge is faulty. Try another tube to see if
it’s the tube or the gauge. Check each tube separately. If differences on the gauge persist with
different tubes connected, repeat the test against another gauge. Only then should a gauge return be
considered.
The gauge will never really need calibration until the difference between the channels is 2% or more. If
you do see a difference greater than 2%, make sure AutoZero is Off, the Time Average is set to 4
seconds and that there is no Baseline reading in the top left hand of the gauge. Only if you see a huge
problem, should send your gauge back for factory calibration.
Pressure dropping to zero in 10 seconds indicates a leak somewhere; try another tube and try the
same tube on a different port to see which piece is faulty. If the tube end is damaged, slice 1/8 inch off
the tube and try again.
To verify the gauge itself, now that you know the tubes are in working order:
To verify the calibration of a gauge, the easiest method is the cross port check shown in Figure 7, which
compares the readings of one channel with respect to the other channel. If the pressures are equal,
then it is likely the gauge is accurate, because the chance of both channels being out of calibration by
the same amount is very small.
Figure 7: Gauge field check configuration: Cross port check, input ports (left) and reference ports (right)
To perform a cross port check
1. Set both channels to measure pressure in Pascals (Pa).
2. Turn Auto-Zero off.
3. Connect the Input port of Channel A to the Input port of Channel B using any tubing that
you know is not blocked or pinched. The measured pressure on both channels should be
within 2% of each other.
4. Disconnect the tubing, and then connect the Reference ports of both channels using the
same piece of tubing. The measured pressure on both channels should be within 2% of
each other.
The same procedure can be followed to compare two gauges. Connect the tube between
corresponding ports on two gauges as shown in Figure 8. The reading on both gauges should be the
same.