As the global market focuses on lean manufacturing, multi-variable sensors that combine pressure, temperature, or other sensors into one package offer the opportunity to reduce the number of components in an installation, trim inventory stock and build times, and eliminate waste. Time spent processing different sensor components is also reduced as fewer process fittings and wire harnesses are required for the overall system—one sensor requires just one connector and one harness.

The Multi-Variable Sensor

While offering two functions, multivariable sensors typically can take on the same features and shapes (thread, housing, and an electrical connection) as traditional single-mode sensors. Combining features into one sensor minimizes the chance of installing the sensor into a wrong port of a manifold or plugged into the wrong connector. While engineers can design OEM systems with different threads and connectors to reduce this risk, the costs associated with these modifications can be higher.

Download this article in .PDF format
This file type includes high resolution graphics and schematics.

For the end user, maintenance and repair associated with multivariable sensors are simpler and faster than they are with multiple sensors. For example, when bleeding refrigerant as part of routine maintenance in refrigeration systems, downtime is reduced as fewer sensors must be removed.  

Design engineers can take advantage of the dual performance of a multivariable sensor in various applications. For example, forklift manufacturers that want to ensure that hydraulic lines don’t freeze and burst can install a pressure/temperature sensor to monitor system pressure while preventing operation until the temperature reaches a specific reading. That same principle applies to hydraulic transmissions in cold climates, where a warm-up period prevents system wear and eventual breakdown.

And by reducing the number of components, there is less potential for failure points in the system design. Improper sensor installation due to cross threading or improper O-ring selection or seating can lead to system leaks and pressure loss. The use of fewer sensors reduces the risk for this type of failure and simplifies diagnosis.

Multi-variable sensors also reduce power consumption requirements. Efficiency in many systems is the name of the game. For example, engineers must consider current consumption in devices that operate on a battery or solar panel. Reducing current consumption increases battery life. A multi-variable sensor typically can operate on less current than two independent sensors. Combining multiple sensing types into one package reduces space requirements as well by eliminating the need for extra fittings and two sensor bodies. 

A Range Of Configurations

While multi-variable sensors historically have focused on the process industry, OEM applications have a growing need and demand for them. Engineers can now choose among multi-variable sensors that combine:

• Pressure and temperature: Hydraulic applications typically require pressure and temperature measurements.

• Liquid level and temperature: By using a submersible pressure transducer with a temperature output signal, multi-variable sensors can closely monitor conditions as well as prevent freezing conditions by activating heaters.

• Pressure and programmable readout: Pressure transmitters can be recalibrated in the field with a display while providing an output signal.

• Differential pressure and temperature: These variables can be used independently or combined to monitor flow (insert calculation).

• Differential pressure and upstream pressure: One device can monitor a filter and pump pressure.

• Pressure and fault condition: A standard pressure transmitter can have a fault condition to fail high or low if the sensor stops working. In a water pump application, if the sensor stops working, it could be beneficial to drop the signal below the normal operating range to stop the pump. 

Greg Montrose is a marketing manager at American Sensor Technologies. With eight years of experience in instrumentation and controls, he has worked on in both sales and marketing functions supporting various industrial, aerospace, alternative energy, and hazardous location projects and applications. He is a graduate of the College of New Jersey (TCNJ) with a degree in international business.

Download this article in .PDF format
This file type includes high resolution graphics and schematics.