Pressure transmitters and pressure transducers

A pressure transmitter, also called pressure transducer or pressure converter, is a pressure sensor, which converts a fluid pressure into an electrical signal of current or voltage. These are the most common pressure transmitters and transducers established in the industry:

• Pressure transmitters with output signal in current (4-20 mA).
• Pressure transducers with output signal in voltage (0-10 V or 0,5-4,5 V ratiometric).

Since measure of pressure is key in most processes, pressure converters and transducers are frequently used in several industries and pressure systems.

How does a pressure transmitter work?

A pressure transducer needs external power supply to operate (VDC).

The fluid pressure enters into the sensor and generates a force on the measuring cell, which includes a Wheatstone bridge of ohmic resistors. These resistors change proportionally to the applied force and generate an output voltage, which is amplified and processed with electronics to generate the standard output signals such as 4-20 mA or 0-10 V.

Pressure transmitter 4-20 mA

A pressure transmitter with current output of 4-20 mA can transmit the signal over long distances with no loss in accuracy. It is also less sensitive to EMC factors.

I_out = 4 mA + (measured pressure / transmitter pressure range) x 16 mA

Pressure transducer 0-10 V

A pressure transducer with voltage output of 0-10 V can transmit the signal to a maximum distance of 30 m, to prevent significant voltage drops in the signal line. The output load must be selected as highly resistive (with typical minimum value of 4,7 kΩ).

U_out = (measured pressure / transducer pressure range) x 10 V

Pressure transducer 0,5-4,5 V ratiometric

A ratiometric pressure transducer has an output signal directly proportional to the supply voltage. It can share the same voltage supply than the one used to power A/D converters, and hence avoid errors due to separate supplies. Ratiometric pressure transducers are primarily used in automotive applications.

U_out = U_v+ x [0,1 + (measured pressure / transducer pressure range) x 0,8 V]

U_v+ = Supply voltage

Accuracy of pressure transmitters and transducers

The accuracy of a pressure transmitter is the deviation of the real output signal from the theoretical ideal line. This deviation occurs due to non-linearity, hysteresis, non-repeatability and zero point offset. It can be defined in two different ways:

• As maximum deviation from the ideal line, for instance ± 0,5% Full Scale (FS) of the pressure range.
• As average deviation from the ideal line, for instance ± 0,25% Best Fit Straight Line (BFSL)

Typically, the average deviation corresponds to half of the maximum deviation.

The accuracy is defined at room temperature and new state.

There are other factors influencing the total error, such as temperature and ageing, which are specified separately.

Hysteresis of pressure transmitters and transducers

The hysteresis specifies the difference of output signal between a rising and falling pressure. It is very low and negligible for Suco pressure transmitters.

Temperature error on pressure transmitters and transducers

The temperature has a significant influence on pressure transmitters, hence the temperature error is added to the accuracy, to calculate the total error of the pressure transducer.

Temperature errors within compensated temperature range are minimized by means of electronics. Outside the compensated temperature range, the maximum error is not defined, however the pressure transmitter still functions.

Non-repeatability error on pressure transmitters and transducers

The non-repeatability defines the reproducibility of the output signal for the same input pressure. For instance if we apply the same input pressure 3 times, the variance between the 3 output values gives the non-repeatability error.

Long-term stability of pressure transmitters and transducers

Ageing affects the accuracy in a pressure transmitter, and its impact on the total error is informed as long-term stability.

Operating voltage and ohmic resistance for pressure transmitters and transducers

All pressure transmitters work with DC voltage and have no galvanic isolation. Within the range specified in the datasheets, the supply voltage may vary without influencing the output signal (the ratiometric transducer is an exception).

In addition, an appropriate ohmic load must be connected to guarantee perfect functioning of the pressure transmitter.

Responsibility in selection of pressure transmitters and transducers

The specifications on medium compatibility cannot be generalized as they pertain to the diaphragm and sealing materials used by the manufacturer. The information cannot be used for all application scenarios.

Testing the suitability of a Suco pressure transducer for a specific application rests under the responsibility of the user. It may be the case that suitability can only be verified with appropriate field-testing.

SUCO pressure transmitters and transducers

Suco pressure transmitters are manufactured in Germany according to highest quality standards. Suco pressure transducers are designed for the most challenging applications, providing exceptional reliability and durability. Please choose your Suco pressure transmitter with the filters offered in this website.