Choosing the right voltage sensor (also known as a voltage sensor) for your application can be difficult because it comes in a variety of configurations. This guide will help you make the right choice.
Each application has unique requirements. To select the right voltage sensor, please compile the following key criteria, as shown in the table and described further below.
Table 1. Key Criteria for Selecting a Suitable Voltage Sensor
Input voltage signal
First, it is essential to understand some things about the voltage being measured, including:
1. What is the expected input voltage range?
2. Is the supplied voltage AC or DC?
3. If it's direct current (DC), is it bidirectional?
4. Is the signal clean or noisy?
We will now explore these issues further.
Input voltage range
Voltage sensors are designed to measure a specific voltage input range. Understanding the input range being monitored will narrow down the choices. The table below shows examples of common input ranges. While not always the case, voltage typically starts at zero and reaches the maximum expected voltage.
When monitoring voltage, it is useful to set up a protective zone around the "expected" voltage to measure potential field conditions. For example, when measuring a 120 V input voltage, it is useful to deploy a sensor that can measure up to 150 V so that "overvoltage" can be monitored when the voltage exceeds the 120 V target.
Input voltage type
When measuring voltage, understanding the voltage type is crucial. Voltage sensors come in various designs optimized for specific inputs. Some designs 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) voltages.
If the input voltage is direct current (DC), is the current always positive or bidirectional? For example, a DC motor might rotate in one direction when a positive current is applied, and in the opposite direction when a negative current is applied. In this case, a bidirectional voltage sensor must be used because many sensors only measure voltages starting from >0 volts.
True RMS voltage vs. Average RMS voltage: Is the input voltage "clean"?
When measuring AC voltage, understanding the purity of the source voltage is crucial. If the source voltage is guaranteed to be pure, either an "average RMS" or "true RMS" voltage sensor can be used. However, if the source voltage may be noisy (common in manufacturing environments), or if the voltage being measured is not a pure sine wave (i.e., a square wave, sawtooth wave, or variable frequency input), a true RMS voltage sensor should be used. In noisy environments, using an "average RMS" sensor will produce erroneous readings.
In both cases, the output will be a measurement proportional to the RMS voltage input, but a "true RMS" voltage sensor will provide a more accurate result.
Output signal type
When selecting the 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. If available, the wider-range 0-10 VDC model is preferable to the 0-5 VDC model because the larger 10-volt output range provides higher resolution measurements than the 5-volt output range.
Depending on the cable length from the voltage sensor output to the control device, you may need to calibrate the maximum voltage, as a long cable can cause a voltage drop. This applies to situations where "voltage" is used as the output signal.
The 4-20 mA output signal provides a DC "current" output signal proportional to the input voltage. When given a choice, design preferences are shown in the table below:
Table 3: Factors to Consider for Output Signal
power supply
Voltage sensors require a power source to operate. This power source can be either a loop power supply or an external power source. Choose a power source that is both readily available and convenient.
24 VDC loop-powered devices require a 24 VDC power supply connected in series with the output signal loop. Sometimes, the output device (such as a PLC) will be internally powered; otherwise, the 24 VDC power supply must be connected in series with the output. NK Technologies' VTR series AC voltage sensors use a loop-powered 24 VDC.
The 24 VAC/VDC device supports 24 VAC or 24 VDC and has a separate power input connection, as shown below.
DIN rail or panel mounting options
It is common to install voltage sensors within distribution boards or control panels. Well-designed voltage sensors not only support direct screw mounting to the panel but also direct connection to DIN rail mounts within the control panel.
DIN rail mounting
DIN rails are long metal strips used to mount components to equipment cabinets or frames. They can securely hold components such as circuit breakers, power supplies, sensors, transducers, and control devices within panel cabinets or frames.
NK Technologies voltage sensor housings easily snap into common 35mm "top cap" DIN rails (TS35 or EN50022). 35mm refers to the rail width from edge to edge.
The voltage sensor housing has a built-in clip that secures it to the DIN rail. To remove the sensor from the DIN rail, slide the clip off the rail to loosen the housing.
Panel mounting
The sensor housing can also be directly mounted onto the housing using two or four mounting holes, and then the housing can be directly fixed to the inner panel with screws or bolts.
UL/cUL certification and CE
When selecting a voltage sensor, products with UL/cUL certification can help verify that they have passed safety testing by an external laboratory. All NK Technologies voltage sensors bear the CE mark.
