Problem:
If, for instance, a valve is closed very quickly, thus shutting off the pipe completely, then the pressure in the pipe falls suddenly to zero. This creates a shock wave that propagates at the speed of sound in the medium against the direction of flow. The shock wave is reflected at the container output, runs back to the valve input, is reflected again, and so on.
The superimposition of the shock wave and its reflections in both directions causes a sharp rise in pressure.

This increased pressure is known as a pressure spike. It can be many times higher than the operating pressure, and thus cause destruction of the sensor.

Pressure sensors can be damaged by pressure spikes.
Pressure spikes are often not noticed.

Solution:
Extra code 591 - restrictor in the pressure channel

The restrictor is welded into the pressure channel.
The restrictor only lets the pressure pass through a restricted orifice, in a zigzag path. This reduces the energy of the pressure peaks arriving at the sensor membrane.

Application tips:

• This problem does not arise with gases, only with liquid media, such as water, hydraulic fluids, beverages
•  It is usually associated with valves and pumps

Caution:

• The pressure channel may become blocked by viscous media, calcification or deposits
• The measuring signal response will become somewhat slower (milliseconds)

Why?
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.

Which instruments?
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

The damping (parameter P4) is used to stabilize the output signal for measurements that are fluctating too rapidly.
This function is similar to the filter in our electronic controllers.

Example: Filling level measurement
Waves on the surface of the liquid can cause fluctuations of the measured value.
Damping can be used to stabilize the measurement.