Common errors in pressure measurement and how to correct them
01 June 2018
STS Sensors: Uncertain output signals, zero offsets or even the complete failure of the measuring instrument are symptoms that can quickly strain the nerves of users. The good news is that when the cause is correctly identified, these errors can often be easily corrected.
In the following, we show you a number of typical errors that users may encounter in practice, but which can usually be avoided with just a little background knowledge. Incidentally, we have already published detailed articles on many of the topics here, which are linked below at the appropriate point.
| Error | Cause | Troubleshooting |
| No output signal |
Line breakage |
Check the cable for damage and ensure that it is properly laid. |
| Wiring error | Check the plug-cable assignment and, if necessary, consult the installation and operating instructions. | |
| Wrong polarity | ||
| The display indicates too low a pressure | Inlet pressure too low due to a blocked port opening |
|
| Pressure transmitter is leaking at the process interface | Check the seal, as it is either too loose or defective (with a new seal, check for media compatibility). | |
| The signal is constant but does not exceed a certain value even when the pressure increases | The bore opening is blocked |
|
| The medium temperature is too low (below -40 °C / -40° Fahrenheit) | The measuring cell of a piezoresistive pressure sensor contains a transfer fluid. This can solidify at temperatures below -40 °C. In this case, a pressure transmitter optimized for low temperatures must be selected, with, for example, the AS100 filling fluid (for temperatures down to -55 °C). | |
| The output signal indicates a high value and remains unchanged | The permissible measuring range has been exceeded. If the pressure sensor operates in the overload range, it will not yet fail, but does not display accurate measurement results. The output signal has reached saturation point and cannot exceed this any further. | A pressure transmitter suited to the measuring range must be selected. |
| The output signal is too low and does not exceed this low value despite a pressure increase | The inlet pressure is too low | The port opening is blocked (see above). |
| Too high a load for mA signals (the electronics connected to the pressure transmitter take too much current) | For mA signals, reduce the load according to the data sheet /operating instructions. | |
| Too low a load for V signals | Increase the load according to the data sheet/ operating instructions. | |
| Operating voltage too low | Operating voltage must be increased in accordance with the operating instructions. | |
| Too wide a measuring range of the pressure transmitter | An instrument corresponding to the measuring range must be selected. Rule of thumb is the measuring range should be ca. 75% of device capability. | |
| Zero offset (the zero point signal is too high) | The membrane has been deformed by impermissibly high overpressure |
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| The membrane is deformed or ruptured by pressure peaks | ||
| Too high tightening torque on installation (measuring cell damaged) | This problem is more likely to occur with instruments of a low pressure measuring range. Pay attention to maximum torque during installation at the process (consult mounting instructions). | |
| The output signal shifts greatly under temperature influence | There is a blockage to the relative pressure compensation (mostly in devices with low measuring ranges up to 25 bar) | The relative pressure compensation should be checked for contamination. It should also be ensured that the installation was carried out correctly. |
| Strongly fluctuating output signal (flickering) | Loose contact | A cable break or a loose plug can be the cause. |
| Strong vibrations or shock pulses in the process | The sensor is resonating. Ideally, the permissible shock load should be checked in the data sheet before selecting a pressure transmitter. Shock-resistant devices are characterized by sealed electronics and do without adjustable potentiometers (such as the ATM.1ST). The problem can be solved later by decoupling the measuring device via a flexible pressure line. | |
| The output signal has interference pulses | There is too much EMC interference | It must be ensured that the cables are shielded. EMC phenomena can be mostly eliminated with careful installation. |
| Differing potentials between measuring instrument and process | Check the ground connection of the pressure transmitter. | |
| The output signal fails after some time in operation | The electronic components fail due to a too high operating temperature | The process medium can be sufficiently cooled via a temperature decoupler, such as upstream cooling fins or a cooling section. A siphon is the best solution for steam applications. |
Some of the errors listed here are due to incorrectly selected pressure transmitters. To avoid errors, you should know in advance as precisely as possible the requirements for the measuring instrument with regards pressure measurement range and installation (a short guide to the correct transmitter selection can be found here). A detailed consultation beforehand with the manufacturer can help spare your nerves. But we’d also be glad to assist you further.
STS Sensor Technik Sirnach AG
Rütihofstrasse 8
8370 Sirnach
Switzerland / Europe
Tel.: +41 71 969 49 29
Fax: +41 71 969 49 20
Email: sales@stssensors.com
Web : www.stssensors.com
