Zeroing of pressure instruments
Adjusting the zero point is important when high accuracy is required.
The zero point signal of a pressure transmitter can shift:
- when it is installed, because of the mounting position or mechanical strain on the pressure connection,
- in operation, because of temperature changes,
- over a long time, because of aging.
Long-term stability (the maximum signal drift per year) is a quality parameter which must be specified in the data sheets.
When, how often?
If high accuracy is required, JUMO recommends
- adjusting the zero offset signal during commissioning, after the instrument has been installed
- and subsequently according to requirements (e.g. every 12 months).
For certain installations, such as in power plants, regulations demand a documented check of the zero offset signal.
Zero offset adjustment is only possible on the more sophisticated instruments:
JUMO dTRANS p02 series: digital, via keypad or the HART interface
JUMO CANtrans series: digital, via CAN interface
JUMO dTRANS p30 series: analog, by potientiometer
JUMO MIDAS series: no zero adjustment possible
What is the zero point?
for absolute pressure: absolute vacuum (0 bar absolute)
for relative pressure: atmospheric pressure (0 bar relative)
for differential pressure: both pressures are equal
Multi-way valves for easy zero point adjustment
The use of a multi-way (manifold) valve enables test and adjustment in normal operation, i.e. on site, without any dismantling:
for absolute pressure: 2-way valve (for connection to a vacuum pump)
for relative pressure: 2-way valve (open to theatmopheric pressure)
for differential pressure: 3-way or 5-way valve