Retrotec DM-2A Instrukcja Użytkownika Pobierz pdf (Strona 45)

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7 Troubleshooting

After getting a clear understanding of what pressure is and how it's measured, knowing the common

causes of erroneous readings will increase the confidence of the results. It is often assumed the gauge

must be regularly calibrated in order to get accurate readings, but this thought obscures the fact that

most gauge problems do not result from incorrect calibrations. The following list provides

approximate percent probabilities based on our experience for certain types of gauge problems.

Notice that gauge calibration is one of the smallest, and even that can usually be eliminated, by

following the gauge check procedures in this manual.

Problem caused by

Error frequency

Error range

Comments

Tubing is crimped shut

25 to 90%

Usually noticeable because gauge does not move,

but the blockage may be partial, which could cause

an erroneous result.

Water in tubing

10%

75-90%

Possible only in wet areas. If gauges sent in to be

repaired or calibrated, the water evaporates and

the user never discovers the cause.

Improper Device selected

20 to 90%

Not common because the wrong Flow Ranges will

appear on the gauge.

Improper Flow Range selected

5 to 25%

50%

Very common unless gauges checked before and

after tests to ensure the right Flow Range.

Extrapolation pressure set

incorrectly

10%

25%

If the gauge shows a different extrapolation

pressure [@ Pressure] then the results will be

extrapolated to the wrong pressure

Improper use of reference tube

for pressurization.

25%

Pressurization is seldom used, but if the technician

is improperly trained, they may not set the

equipment up properly for this test.

Time averaging set too high or

too low

25%

5 to 10%

If the gauge is fluctuating too much it will be

difficult to read. If the time averaging is too high,

the pressure may have changed but that change is

not reflected in the reading.

Wind

25%

10%

These errors can be eliminated by long-term

averaging or by multiple pressure pickups.

Out of calibration

1-50%

Gauges can go out of calibration in a week or may

take 10 years. It is impossible to tell unless the

readings seem unreasonable.

Out of calibration with regular

checks

0.5%

1-2%

Regular gauge checks can eliminate most of the

calibration problems, by identifying large errors

immediately, and before erroneous test results can

be taken. It is unlikely that errors in excess of 2%

would occur if the gauges checked before each use.

Proper training can eliminate almost all of the above errors.

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