Retrotec DucTester 341 - Manual (Page 63)

Page 63 of 83
©Retrotec Inc. 2014
14. Field Check the DucTester to find out what is not working
Standard procedure says you calibrate your gauges every year or two, but does this really make sense?
The gauge can be calibrated regularly but when did the gauge go out of calibration? Last week or last
year?
There is a quick way to field-check your gauge regularly or before an important test. Gauge calibration,
where errors are typically a few %, is not as frequent a cause of problems when compared to blocked,
leaking or pinched tubes that happen more often and can yield errors of 10 or 90%. Sending your gauge
in for calibration does not address those problems but doing a field check will.
14.1 Field Check the gauge
To verify the calibration of a gauge, the easiest method is to compare 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.
To perform a cross port check
Download the Pressure Gauge Operation Manual for DM32 from:
http://retrotec.com/sites/default/files/manual-guides-specs/Manual-DM32%20Operation.pdf
and look at the Section named “Verify your gauge accuracy between factory calibrations”.
You will also Field Check the tubes using the procedure outlined there.
This test requires one color of tube be connected between channel A and B. If both channels don’t
display the same pressure or the pressure drops rapidly the tubes are blocked or leaking. Water can be
whipped or blown out of tubes and crimped tubes can be adjusted.
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.
Pressure dropping to zero in 10 seconds or less indicates a leak somewhere; try another tube and try the
same tube on a different port to see which piece is faulty, the tube or the gauge. If the tube end is
damaged, slice 1/8 inch off the tube and try again.
The tubes have now all been checked, removing that major source of error.
14.2 Field Check the DucTester as a system
This check will ensure that the DucTester is connected properly, and will ensure that the measured
results for flow are within 10% of the true value when using the DucTester as a system with Flex Duct.
The flow verification plate is optional equipment, since a temporary one can be easily manufactured
using thin, solid, cardboard with a 4" x 4 5/8" square hole (18.6 sq in) cut in the center. If making your
own, a 1/4 inch diameter hole should be made in one corner of the plate, as far away from the larger
hole as possible, into which the blue tube can be inserted.
To field check the DucTester calibration