Almost everyone uses the terms pressure sensor, pressure transducer, and pressure transmitter interchangeably, and that’s okay!
What‘s in a name? When it comes to electronic pressure sensing, the answer for many users is “not much.” Manufacturers do not always or consistently differentiate between pressure transducer and pressure transmitter, while some devices are simply called pressure sensor. It’s easy to see why, as all three terms refer to functionally similar instruments that measure and convert the physical property of pressure into an electronic signal.
Other names for electronic pressure measuring instruments includes I/P (current to pressure) converters and I/P transducers, P/I or P to I (pressure to current) converters, pressure senders, and pressure switches.
Some of these are legacy terms, part of the industry’s or manufacturer’s history, while for certain users it’s a matter of personal preference. It’s little wonder that the market tends to lump together all devices with a wire and refer to them all as simply pressure sensors!
The Types of Electronic Pressure Measurement Instruments
The textbook definition of transducer is an instrument that measures pressure, load, force, or other states, and converts the reading into an electronic signal. A transmitter also converts a reading into an electronic signal, but it then amplifies, modifies, and sends that signal to a receiver. A switch is a device that, based on a preset switch point, interrupts the current or diverts the current from one circuit to another.
At WIKA, a transducer (like the TTF-1) has a non-amplified output, while a transmitter (like the A-10 or
S-20) has an amplified output. Other electronic pressure devices are simply called a sensor, as this is an easy way to refer to next-generation instruments like the A-1200 with IO-Link or the MH-4-CAN with CANopen and SAE J1939 CAN communication protocols. All the above electronic pressure measuring instruments are listed under the category pressure sensors, while pressure switches are grouped separately.
Comparing Pressure Transducers and Transmitters
In a pressure transducer, a thin-film or piezo-resistive pressure sensor is mounted on a process connection. The transducer converts pressure into an analog electronic output signal, typically as a millivolt per volt output. These signals are not linearized or temperature compensated.
A pressure transmitter has additional circuitry that linearizes, compensates, and amplifies the signal from a transducer. The different signal types are typically voltage signals (e.g., 0 to 5 or 0 to 10 volts), milliamp (e.g., 4 to 20 milliamp), or digital. The instrument then can transmit the signal to a remote receiver.
Many pressure transmitters offer a variety of calibration options, including turndown and zero/span adjustment. Smart transmitters can be calibrated, tested, and reset remotely using a bus network.
Pressure Transducer or Transmitter: Which One to Choose?
Despite the amplified vs. non-amplified differences between transmitters and transducers, it really doesn’t matter what people call them or which ones they use. What’s more important is whether the device suits a particular application and offers the needed output. Accuracy, range, working temperature, and the medium are all determining factors when selecting the right pressure instrument for an application.
As for the output signal, here are some factors to take into account:
- Typical mV outputs do not have temperature characterization.
- A current signal is more immune to interference and noise than a voltage signal.
- A current signal can also travel farther.
- An analog signal is just the pressure reading.
- A digital signal allows a user to collect more information and other variables besides pressure.
- The input card of many control systems accepts only amplified signals.
The bottom line: Get the pressure device you need, regardless of what it’s called. For expert advice on the best sensors to use with your particular application, contact the pressure measurement professionals at WIKA USA.