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Measurement Signal

Measurement Signal Selection

A guide to measurement signal types for sensors & instrumentation, including explanations, applications and choice of products with analog & digital signals.

Select a sensor or instrument by input or output signal type. Measure or transmit current, voltage, RS232, RS485, USB, solenoid relay switch and logic switch.

  • 4-20mA Output Hydrostatic Level Transmitters & Sensors - Explore industrial 4-20mA hydrostatic level transmitters for reliable liquid depth measurement. Ideal for tank gauging, borehole control & process monitoring applications.
  • USB Pressure Sensors - Choose USB pressure sensors offering direct computer connection via USB for power, communication, and data logging. Ideal for labs, test rigs, and calibration.
  • HART® Liquid Level Transmitters - Discover smart liquid level transmitters featuring the HART protocol for enhanced diagnostics & configuration over standard 4-20mA wiring in process control.
  • 4-20mA Output Pressure Sensors - Find reliable pressure sensors with 4-20mA current loop outputs. Designed for demanding industrial applications, offering excellent noise immunity and simplified 2-wire installation for process monitoring.
  • HART® Pressure Transmitters - HART pressure transmitters for configuration via a distributed control system (DCS) or HART communicator.
  • 0-10 Volts Output Pressure Transducers - 0 to 10 volts output pressure transducers with amplified signal conditioning electronics and 3 or 4 wire configuration for generating a 0-10Vdc analog signal which corresponds to a specified pressure range.
  • TPSA Precision High Pressure Transducer 0-5 Volts Output Pressure Transducers - 0 to 5 volts output pressure transducers with amplified signal conditioning electronics and 3 or 4 wire configuration for generating a 0-5Vdc analog signal which corresponds to a specified pressure range.
  • AS Autosport Pressure Transducer Ratiometric 0.5-4.5 Volts Output Pressure Transducers - Ratiometric voltage output pressure transducer with a 0.5 to 4.5 volt signal which is proportional to the nominal input supply voltage of 5 volt dc.
  • RS485 Serial Interface Pressure Sensors - RS485 output pressure sensors for incorporating into digital sensor networks. These sensors can be allocated a unique device address and connected in series to other sensors with RS-485 serial interfaces on the same communications link.
  • TPSADA Digital Auto-Zero High Pressure Sensor 1-5 Volts Output Pressure Transducers - 1 to 5 volts dc output signal pressure transducers with a 4 volt output span proportional to the specified pressure range, with a 1Vdc output signal at the lowest input pressure and 5Vdc output signal at the highest input pressure.
  • I²C Serial Interface Sensors and Instruments - Explore a range of I²C equipped sensors and instruments designed for seamless integration into your industrial or research projects.
  • SDI-12 Serial Interface Sensors and Instruments - Explore a range of robust SDI-12 sensors and instruments designed for integration with environmental data acquisition systems.
  • 0-20mA Output Pressure Transmitters - 0 to 20 milliamp output pressure transmitters with a 3-wire configuration for installations where the positive voltage supply is separated from the current loop signal wires.
  • RS232 Serial Interface Pressure Sensors - RS232 compatible pressure transducers for linking to PC computer serial ports.
  • 0-10 Volts Output Hydrostatic Sensors, Probes & Transducers - Analog output hydrostatic sensors with a 0 to 10 volt amplified output signal for measuring liquid head pressure or fluid level.
  • Modbus Communications Protocol Pressure Sensors - Pressure sensors with Modbus communications protocol for connecting to a serial bus or a digital sensor network.

When selecting a sensor or instrument, the signal type is a primary consideration. For analog signals, engineers must determine if their application requires a current (typically 4-20mA) or voltage (e.g., 0-10V) output. The choice often depends on the distance the signal needs to travel and the susceptibility to noise. Current signals are generally more robust over longer distances.

For digital signals, common options include RS232, RS485, and USB. RS232 is suitable for shorter distances and point-to-point communication, while RS485 is designed for longer distances and multi-drop networks. USB offers high-speed communication and is commonly used for data acquisition and configuration.

Beyond these, some applications may involve discrete signals, such as those from solenoid relay switches or logic switches, used for on/off control or status indication. Understanding the specific requirements of your data acquisition system, including the type of input it accepts, is essential.

A common challenge arises from overlooking the specific power requirements of different signal types. While some sensors and instruments are tolerant of minor voltage fluctuations, others, particularly those with sensitive electronics or those used in precision measurement applications, require a clean, regulated power supply. Variations in voltage or the presence of noise on the power line can introduce errors into the measurement signal.

Another frequent issue stems from incorrect shielding practices. While shielding is essential for protecting signals from electromagnetic interference, improper implementation can actually exacerbate noise problems. If the shield isn’t correctly grounded at one end only, it can create ground loops, which act as antennas and pick up even more noise. This can be particularly problematic with low-level analog signals.

Wiring configurations also deserve careful attention. For example, 4-20mA current loops, a common industrial standard, can be implemented in either a two-wire or three-wire configuration. Understanding the differences between these configurations and selecting the appropriate one for the application is critical. A two-wire system draws its power from the loop itself, while a three-wire system has a separate power supply. Using the wrong configuration can lead to communication failures or damage to the devices.

Finally, neglecting the importance of proper cable selection can also introduce problems. The type of cable, its shielding, and its length can all affect signal quality. Using the wrong cable for a particular signal type or application can result in signal attenuation, noise pickup, and even crosstalk between different signals.

Question & Answers

Find answers to questions about analogue and digital measurement signals used to transmit readings from measurement instrumentation.

Analogue vs digital signal usage

Do most sensors have an analogue output?

Yes and no, but typically all sensors start with an analogue signal of some kind , the  transducer but normally its too weak a signal to transmit far and is uncompensated for environmental changes. A signal conditioning unit (SCU) compensates and converts the signal to something more universal like RS485, 4-20mA, 0-10Vdc , Modbus, IO-Link, or i2c.

Analogue is still dominant on long cables of say 20-100m, but digital is becoming much more common inside instrumentation and packages, and digital interfaces such as RS485 can be used over much greater distances without data corruption. Sensors on production road vehicles for instance, are becoming all digital, typically use the CANbus digital protocol.

Is 0.5-4.5Vdc output proportional to input supply voltage

Many other companies use “Ratiometric” to describe a pressure transducer with a “0.5 to 4.5 Vdc” output signal. Does it really mean that the output signal is proportional to the input supply and why is it not specified as a sensitivity in mV/V?

mV/V senstivity is used to describe the output of a strain gauge output type device, e.g. 2mV/V, the output is typically much smaller than the input voltage hence the Millivolt to Volts ratio. 0.5 to 4.5 V output is an amplified output where the output is comparable to the input voltage which is typically 5Vdc.

Also on some circuits there is a limitation on the supply voltage e.g. 5V +/-0.5V, and a mV/V description of the output is more suited to describing outputs that can be used with a wide range of supply voltages. However a change in input voltage within those limits of constraint will directly affect the output hence the term “ratiometric”, whereas an input supply that is regulated will maintain a constant output.

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