Control systems are becoming increasingly intelligent and complex, and sensor technology must keep pace to meet application requirements. Gone are the days of sensors that require signal conditioning and calibration work. You no longer need to worry about the functionality of the sensor when it comes to sensor design, implementation and application. Given the importance of sensors as pressure measurement devices, and the variety and quality of sensors on the market, you must choose carefully.

Overview of Possible Solutions

Before making a sensor purchase list, it is important to review the various application options. Consider what alternatives are available and how they meet the requirements and specifications of your own design. As mentioned earlier, control and monitoring systems have changed dramatically over the past few decades, primarily due to increased design complexity. These changes include manual systems becoming control systems based on electronic technology, multiple components becoming highly integrated products, and increased attention to cost issues. There are multiple solutions for heavy-duty applications, what are the heavy-duty environments? Here are just a few specific examples, such as environments with a wide temperature range (e.g. -40 °C to 125 °C [-40 °F to 257 °F]), harsh media such as refrigerants, oils, brake fluids, hydraulic fluids, and environments using compressed air. While these temperature ranges and harsh environments may not be the most extreme, they represent the majority of transportation and industrial environmental applications.

Heavy duty pressure sensors can be used in the following areas:

-For HVAC/R applications to monitor system performance, control compressor inlet and outlet pressures, rooftop chillers, refrigeration chambers, refrigerant recovery systems, and compressor oil pressure.

-For air compressor applications, monitoring compressor performance and efficiency, including monitoring compressor inlet and outlet pressures, filter pressure drop, cooling water inlet and outlet pressures, and compressor oil pressure.

For transportation applications to maintain performance of heavy-duty equipment by monitoring pressure, hydraulic force, flow and level in critical systems such as pneumatics, light-duty hydraulics, brake pressure, oil pressure, transmissions, and truck/trailer airlocks.

The variety and quality of sensor models on the market makes it important to carefully examine the options. The products should be analyzed for reliability, calibration, zero point compensation, sensitivity, and total error range.

In HVAC/R applications, heavy-duty sensors are used to control compressor inlet and outlet pressures, rooftop chillers, and other recovery and pressure systems.

Selection Criteria

As with most electronics, sensor selection criteria reflect important design challenges. System design requires stable sensors to ensure that the system will function properly at all times and locations. System consistency is also important, as a sensor removed from the box must be interchangeable with any other sensor in the box, and the product must perform as intended. The third criterion to consider is cost, which is a ubiquitous challenge. As electronic devices become increasingly intelligent and accurate, older components of the solution have to be updated. The cost depends not only on the individual sensors, but on the overall cost of the product replacement. Which products are replaced by the sensors? Are operations such as pre-calibration or full compensation performed prior to replacement?

When selecting a sensor for an industrial or transportation application, consider the following factors:

1) Configurability

When using each sensor, consider whether the device is a standardized or customized product? Customization options include connectors, pressure interfaces, reference pressure types, ranges, and output formats. Whether off-the-shelf or configurable, is the product selected easy to meet precise design requirements and available quickly? When you design your product, can you get samples quickly so that the time to market is not delayed or compromised?

2) Total Error Boundaries

The total error range (TEB) (shown below) is an important measurement parameter that is comprehensive and clear. It provides the true accuracy of the device over the compensated temperature range (40 °C to 125 °C [-40 °F to 257 °F]) and is critical to measuring product consistency and ensuring product interchangeability. For example, with a total error range of ±2%, the error is always within 2% of the range, regardless of the temperature as long as it is within the established range, and regardless of whether the pressure is rising or falling.

Often, manufacturers do not list the total error range in the product data sheet, but rather list the various errors separately. When the various types of errors are added together (i.e., the total error range), the total error range can be very large. Therefore, the total error range can be used as an important selection basis for choosing a sensor.

3) Quality and performance

What performance criteria does the product meet? In many cases, sensors are manufactured based on one or two sigma tolerances. However, if the product is manufactured to meet Six Sigma standards, it will have the advantages of high quality, high performance, and good consistency, and thus can be considered to perform in accordance with the product specifications.

4) Other considerations

When selecting a heavy-duty sensor, the following factors should also be considered:

-The sensor must be compensated, calibrated, amplified, and must be a finished product - no additional resources are needed to adapt it to the application requirements.

-Custom calibration, or custom calibration combined with custom output, should be able to output a variety of specified voltages to meet design specifications without changing the design.

-CE compliant, IP rated, long mean time to failure, EMC compliant, and high durability even in harsh environments.

-A wide compensation temperature range allows the same device to be used in all parts of the system for a wider range of applications.

-Multiple connectors and pressure interfaces allow the sensor to meet the needs of a wide range of applications.

-Small size makes the sensor more flexible in placement

-Sensors should meet industry standards such as ISO 9001

-The overall cost of the sensor needs to be considered, including integration, configuration and implementation costs.

Another major factor to consider is design and application support. Is there someone available to answer important questions for design engineers during the design, development, test and production phases? Does the supplier have sufficient global presence, products, and support to assist the customer's design through to global manufacturing?

The Relt pressure sensor is a highly configurable new pressure sensor for HVAC, refrigeration, industrial and transportation applications. It combines piezoresistive detection and ASIC (Application Specific Integrated Circuit) signal conditioning technology to provide reliable performance even in harsh environments. The sensor has a total error range of ±2% over the operating temperature range of -40°C to 125°C [-40 F to 257F] and is fully calibrated and compensated for its zero point, sensitivity, temperature effects and nonlinearity.

Design engineers are able to make quick and sound decisions based on real, verifiable data by using a complete selection list to choose a heavy-duty pressure sensor. With current sensor accuracy levels far exceeding those of just a few years ago, it is especially important that design engineers are able to quickly select products that can be used without modification.