The Value of Calibration for MEMS Pressure Sensors

Sensors play a huge role in kidney dialysis system

Sensors play a huge role in kidney dialysis systems (Image credits: Aleksandr Ivasenko/shutterstock.com)

The value of a measurement tool is dependent on its accuracy. Measurement devices, like sensors, are found everywhere in automotive, healthcare and industrial settings. For a lot of these applications, it is necessary that the sensors are accurate to ensure quality control and guarantee patient safety.

On the other hand, for Piezoresistive Pressure Sensors, this is a popular choice because of their quick responses, ruggedness, and large range measurements, the changes in temperature influence the pressure output and, eventually, the accuracy. But as long as the dye in a wafer has uniformity, errors that are related with temperature can be corrected, or rewarded.

Pressure-sensor compensation has two popular methods: passive and active. Passive compensation is completed by trimming the resistors while it is being manufactured. It is suitable for environments where the sensor will go through small changes in temperature.  For temperature changes that are more challenging, active compensation utilizes an on-board circuit, or a microcontroller.

This is where the temperature of the pressure sensor’s immediate surroundings is regularly measured by the temperature sensor. It then moves it to the on-board circuit to correct any errors that are temperature-related also known as offset.  This also allows near-zero temperature errors and greater operating ranges, making it an engaging quality for high-quality pressure sensors.

Calibrate It Yourself or Buy It Calibrated

Sensor calibration has two possible options: 1) the sensors in the manufacturing line is calibrated by the pressure-sensor customer or 2) the pressure-sensor manufacturer’s fully compensated; pre-calibrated sensor is integrated by the customer.

There are a few good reasons why pressure-sensor customers might want to calibrate their own sensors.  One reason is that they might already have a microcontroller in their final product, for example, on a board-mountable part.  In situations like this, the active calibration can be completed with the microcontroller.

A customer might also have a sensor-packaging/housing process that puts a large amount of stress on the sensor. When this happens, the pressure sensor that is already calibrated would register additional pressure through the stress-inducing packaging process. The increased pressure would then introduce a new zero point.

One drawback of customers doing their own calibration is that in-line calibration can be difficult to perform and it can be highly disruptive too. Another issue is that purchasing an already-calibrated sensor would cost less than to acquire in-line calibration that would require specialized equipment and expertise.

Most important of all the drawbacks is the time the calibration would require if the customers were to do it on their own. Mass calibration cannot be done as each sensor requires individual calibration. In addition, the temperature range required for calibration means that the equipment takes a long time to reach the required temperature extremes.

Purchasing a fully compensated pressure sensor from a manufacturer, like Merit Sensor, will be more expensive compared to an uncompensated sensor. It is important to weigh this, however, against how much it would cost if the parts are calibrated in house. Time is money.

Purchasing fully compensated parts from the manufacturer is a way to reduce some of the time and costs associated with calibration issues because calibrated parts can simply be plugged in line as required.

This is ideal for companies who want to move products through production faster, particularly those who don’t have the equipment, skill, and process flow to hold in-line calibration. It often makes sense for the pressure-sensor manufacturer that has its own calibration professional, tools, and expertise to do the calibration.

Custom Sensing Solutions

The LP series is one of the various ranges of pressure sensors offered by Merit Sensor for ultra-low-pressure applications. This type of sensor is ideal for applications such as Continuous Positive Airway Pressure (CPAP) machines because of its suitability for use with non-corrosive gases. The LP series offers a pre-calibrated option which means that the pressure sensor is instantly accessible for medical use. It is also suitable for industrial use, in air-filtration systems and spirometry measurements in healthcare.

Merit Sensor offer the PMD series for applications that need low to medium pressures. The PMD series is suitable for use with air and other non-corrosive liquids. It is also capable of measuring differential, absolute, and vacuum pressure. This series is the most ideal pressure sensor for ink level monitoring in printers and can work over 0.34 to 3.5 bar pressure range.  For this application, the calibration is fast and straightforward because it uses an external microprocessor. This means that the uncompensated PMD series is really a popular option.

The TVC series, on the other hand, is suitable with harsh media operations such as high-temperature oil.  The sensor is an excellent choice for the automotive industry because of its high level of media resistance. The device’s radial sealing means it can be integrated at a module level with a minimal introduction of stress.  

TVC Series Sensor from Merit Sensor

TVC Series Sensor from Merit Sensor

Fully compensated sensors are widely preferred in automotive applications for the reason that they save automotive manufacturers from integrating calibrations that are time-consuming, over a wide temperature range, into their production processes.

For the past 25 years, Merit Sensor has gained so much experience specializing in Piezoresistive Pressure Sensors. It is a very good choice for customers who need pressure sensors for their applications. It offers standard and custom solutions for a wide selection of applications. Merit Sensor can also supply components that are either uncompensated, passively compensated, for use over a narrow temperature range, or fully compensate, for use over a wide temperature range.

Merit Sensor can help if the customers are not sure which solution is the most appropriate to use. All of Merit Sensor’s products come with on time, personal, and trained support in order to find flexible and innovative solutions to get customers’ products to market.

This information has been sourced, reviewed and adapted from materials provided by Merit Sensor.

For more information on this source, please visit Merit Sensor.

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