A small amount of drift is acceptable. This type of drift is usually caused by the unit displaying a value that falls in between two digits. Example: You apply 50.5 PSI to the DPM 3, and the reading bounces between 50 psi.and 51 psi. This would be considered normal. If the unit drifts from zero and the displayed readings drift more than one or two counts, the offset my simply need to be zero'ed out, or there may be a problem with the way the DPM 3 is being used, or with the unit itself.
To zero the DPM-III, set the pressure Selector Switch to the pressure range to be measured, then make sure that the DPM-III is vented to atmosphere (room air), and turn the front panel Zero Knob so that the display reads zero pressure. (the DPM-III may take a few seconds to settle to zero when first turned ON).
If the DPM 3 display is stable when the unit is vented, but drifts when it is connected to your pressure/vacuum source, then the problem may be caused by fluctuations in the tubing being used to connect your pressure source to the DPM 3. Avoid use of surgical tubing that can expand and contract with pressure fluctuations. Drift can also be caused by temperature fluctuations in a closed pneumatic system. Use of a three-way Luer-Lok stopcock at the DPM 3 inlet provides a convenient way of venting the DPM 3 and releasing any built-up pressure or vacuum.
Another possible cause is that the drift may originate in the device being measured. If possible, substitute a known-good pressure source. Doing so may help you determine where the problem is.
Excessive drift is occasionally a symptom of transducer contamination. Saline or mineral deposits, or a small piece of debris, can lodge itself inside the pressure transducer. If your DPM 3 drifts more than one or two counts when it is vented, you may have debris in the transducer. This becomes more likely if you're using hard tap water or saline during your measurements. You can try to dislodge the debris by irrigating the transducer assembly. This possibility becomes more likely with an older unit
- Fill a syringe (30 mL or so) with distilled water.
- Connect a piece of tubing to the syringe end. Use tubing small enough to be easily inserted into the DPM 3 inlet port.
- Insert tubing ½" or so into the DPM 3 pressure inlet; gently irrigate.
- Empty the syringe into the DPM 3. Hopefully, when the water exits the transducer assembly, the offending debris will be removed with it.
Please contact the Technical Assistance Center if the above suggestions fail to resolve the problem.