by NK Technologies
Choosing the right voltage transducer (also called a voltage sensor) for your application can be daunting since it comes in many configurations. This guide will help you make the right choice.
Each application will have unique requirements. To choose the correct voltage transducer, gather the following key criteria, shown in the table and described further below.
Input voltage signal
To get started, a few things must be known about the voltage being measured, including:
- What is the expected input voltage range?
- Is the supplied voltage AC or DC?
- If direct current (DC), is it bidirectional?
- Is the signal clean or noisy?
Each of these will be explored further below.
Input voltage range
Voltage transducers are designed to measure specific voltage input ranges. Knowing the input range being monitored will narrow down the options. The table below shows a sample of common input ranges. Although not always the case, voltages often start at zero and reach a maximum expected voltage.
When monitoring voltage, it is useful to have a guard band around the “expected” voltage to measure what might occur in the field. For example, when measuring 120 V input voltage, it is useful to deploy a transducer that can measure up to 150 V so that “over-voltage” conditions can be monitored when voltage exceeds the 120 V target.
Input voltage type
Understanding the voltage type is critical when measuring voltage. Voltage transducers have numerous designs and can be optimized for specific inputs. Some are designed to measure alternating current (AC) only, while others are designed to measure direct current (DC) inputs. More advanced devices can measure both AC (VAC) and DC (VDC) voltage.
If the input voltage is direct current (DC), will the current always be positive, or is it bidirectional? For example, a DC motor may rotate in one direction when a positive current is applied and the opposite when a negative current is applied. A bidirectional voltage transducer must be used in this situation since many transducers only measure voltage starting at > 0 volts.
True RMS voltage vs average RMS voltage: is the input voltage “clean”?
When measuring AC voltage, it is essential to know how clean the source voltage is expected to be. If a clean sinusoidal source is guaranteed, you can use either an “Average RMS” or “True RMS” voltage transducer. However, if the source voltage may be noisy, as is typical in a manufacturing environment, or if the measured voltage is not a pure sinusoidal wave (i.e., square wave, sawtooth wave, or variable frequency input), then a True RMS voltage transducer should be used. An “Average RMS” transducer in a noisy environment will produce false readings.
In both cases, the output will be a measurement proportional to the RMS Voltage input, but a “True RMS” Voltage Transducer will provide more accurate results.
Output signal type
When choosing an output signal, there are two voltage-based options and one current-based option.
The 0-5 VDC and 0-10 VDC output models provide a DC output “voltage” (VDC) proportional to the input voltage. When given a choice, the wider range of the 0-10 VDC model is preferred over the 0-5 VDC model as the larger 10-volt output range provides higher resolution measurements than the 5-volt output range.
Depending on the cable length from the voltage transducer output to the control device, you may need to calibrate the maximum voltage due to the voltage drop induced by long cable runs. This applies when using “voltage” as the output signal.
A 4-20 mA output signal provides a DC “current” output signal proportional to the input voltage. When given a choice, the design preferences are shown in the table below:
Power supply
Voltage transducers require a power source to operate, provided as either loop-powered or, more often, an external power supply. Choose a power source that is both available and convenient.
24 VDC loop-powered devices require that 24 VDC power be supplied in series with the output signal loop. Sometimes, the output device (e.g., PLC) will supply the power internally; otherwise, 24 VDC power must be wired in series with the output. The NK Technologies VTR Series AC Voltage Transducers use loop-powered 24 VDC.
24 VAC/VDC devices support either 24 VAC or 24 VDC and have a separate power input connection, as shown below.
DIN Rail or Panel Mount Options
Mounting a voltage transducer inside an electrical panel or control panel is common. A well-designed voltage transducer will support screw mounting directly to the panel but will also accommodate attaching directly to a DIN rail mount within the control panel.
DIN rail mounting
DIN rails are long metal strips used to mount components onto equipment cabinet racks. They securely fasten components such as circuit breakers, power supplies, sensors, transducers, and control devices inside a panel cabinet or frame.
NK Technologies voltage transducer cases easily snap onto common 35 mm “Top Hat” DIN rails (TS35 or EN50022). The 35 mm refers to the rail width from edge to edge.
The voltage transducer cases have built-in clips that snap onto the rail. To remove the transducer from the DIN rail, slide the clips away from the rail to release the case.
Panel mounting
The transducer case can also be panel mounted directly to the case by using the two or four mounting holes and either screw or bolt the case directly to the inside panel.
UL/cUL listing and CE
When selecting a voltage transducer, a product with a UL/cUL listing can help validate that it has been tested for safety by an outside laboratory. All NK Technologies voltage transducers carry the CE mark.
Leave a Reply