Choosing the Right Switch Or Sensor

The correct switch or sensor choice for a particular application is often an area that is given too little attention. With varieties of environments and signal voltages and currents, the choice for the switch or sensor is particularly important to choose correctly as the longevity of the device is often determined by this choice

Match Your Application

Determining the application for the device before selecting a switch or sensor is extremely important. As you will see, there is a large variety of devices to choose from, however the choices are often reduced greatly by first determining the application’s specification. Some of the criteria to consider in choosing a device are:

Voltage and Current

Switches and sensors can operate in a wide range of voltages. Each switch and sensor has an optimum voltage and current that needs to be considered.

• On the DC (direct current) voltage side, there is8VDC, 12VDC, 24VDC, 48VDC and even higher to DC voltages that can be as high as 124VDC.
• On the AC (alternating current) voltage side, there is 12VAC, 24VAC, 48VAC, 110VAC, 220VAC and higher.

Determine the application. Are the switches driving relays, illuminating signal lights or running signals back to PLCs  and DCS. In general, unless the switches are used as control relays carrying the full load of the device, feedback signals generally have low current loads. (less than 1.0 Amps).

The most common signal type in North American is generally 500 mA at 120 VAC , with the rest of the applications being 24 Volts or lower DC signals. Often you will find in advanced process control systems where they will use lower voltagse (24V, 12V, or 8V) DC control signals with 200mA or less of current.

Reliability and Longevity

It is important to select your switch or sensor based on the signal type used in the plant or operation control devices such as PLCs, DCS or Networking protocols. In order to achieve a reliable control or feedback signal in the installation, particular attention needs to be matching the proper switch or sensor with the current and signal voltages and currents of the feedback signals.