Problem:
Varying temperatures of the medium and the surroundings, combined with high humidity, can lead to condensation within the pressure transmitter. This in its turn will cause corrosion damage to the electronics or the sensor.
Condensation within a vessel
Occurs frequently in:
Solution:
Extra code 631 - encapsulated version
The encapsulation of the sensor in silicone gel reduces the volume of
air within the sensor so far that it is not possible for sufficient
condensation to arise to the extent that it would cause damage.
Why?
Adjusting the zero point is important when high accuracy is required.
The zero point signal of a pressure transmitter can shift:
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
For certain installations, such as in power plants, regulations demand a documented check of the zero offset signal.
Which instruments?
What is the zero point?
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:
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Problem:
Certain applications, such as CIP processes (CIP = Cleaning In Place) require hygienic process connections with a guaranteed maximum surface roughness RA.
JUMO pressure transmitters with a front-flush connection have an RA less than 0.8 µm. However, special applications require an improved maximum surface roughness RA < 0.4 µm.
JUMO dTRANS p31 with clamp connection
Sectors:
Solution:
Extra code 452 - electrolytically polished
Electrolytically polished process connections have an improved surface roughness RA < 0.4 µm.
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:
Caution:
Intelligent transmitters with digital electronics can already convert
the measurement signal in the sensor from the original pressure unit
into a unit that is better suited to the application.
This serves not only for easier use but also to reduce the processing that has to be performed by other instruments in the measurement system.
Application examples:
for measuring pressure: display in psi or Torr or kg/cm2
for filling level meaurement: display in cbm or liters or cmH20
for flow measurement: display in cbm/h or liters/minute
JUMO instruments with scaling:
The JUMO dTRANS p02 series only applies scaling to the value displayed by the LCD, while the value of the analog output
(in mA) remains unaltered.
The scaling function in the JUMO CANtrans series directly alters the measurement that is transmitted via the digital CAN bus to the control system.
Why?
Adjusting the zero point is important when high accuracy is required.
The zero point signal of a pressure transmitter can shift:
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
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
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The current source function (parameter P8) can be used for manual setting of the mA value at the output of the pressure transmitter to a defined value, regardless of the actual pressure prevailing at the moment.
This saves having a separate current source.
This makes it easy to test the 2-wire current loop circuit.
For example:
The current source function is standard for all HART instruments.
Possible settings:
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3,85 mA
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Underrange |
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4,00 mA
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Measurement range 0% |
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12,00 mA
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-
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Measurement range 50% |
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20,00 mA
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-
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Measurement range 100% |
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21,50 mA
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-
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Overrange |
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.
The final result is the same in both cases.
The second method, using the density adjustment parameter, is easier for the user if the density changes from time to time, as it can then be manually corrected by using the keys on the instrument.
| Medium |
Density
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Filling level
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Measured pressure
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| Water |
1,00 kg/dm3
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10 m
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1,00 bar
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| Benzine |
0,85 kg/dm3
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10 m
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0,85 bar
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Example for Filling level measurement Benzine
Density: 0,85 kg/dm³
Filling level: 10 m
Nominal range: 4 bar (=100%)
Configuration (1): by setting the measurement span (parameter P6)
| Medium |
Density
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Measurement span P6
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Density correction P0
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| Water |
1,00 kg/dm3
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25,00 %
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1.00
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| Benzine |
0,85 kg/dm3
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21,25 %
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1.00
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Configuration (2): by setting the density correction (parameter P0)
| Medium |
Density
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Measurement span P6
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Density correction P0
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| Water |
1,00 kg/dm3
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25,00 %
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1.00
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| Benzine |
0,85 kg/dm3
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25,00 %
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0.85
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