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Measurement Signal

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

Products by Signal Type

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.

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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