Industry standards for optimum sensor specification

8th May 2017
Joe Bush

The sensor market has not reached its full potential yet, and according to a report by the market research firm BCC Research, the market is still expected to grow by more than ten percent by 2020. Leslie Neill, Senior Product Manager, Honeywell Safety and Productivity Solutions, investigates.

In nearly every industry, there is now an increased demand for sensors. This can at least partially be attributed to user demand for more intelligent and connected systems, along with the simple fact that devices are becoming smarter – whether this is a thermostat or complex construction machinery.

Designing and building a connected solution is not as straightforward as implementing more and more sensors into a system without giving it the proper consideration. While it is certainly true that sensors can provide end users with scores of valuable data, they can also cause a system to fail and potentially negatively impact the finances of a business. An inaccurate or faulty sensor is not a cheap piece of equipment to replace, unsurprisingly. It can also be difficult to correct the fault, and in some circumstances the end user’s operation can be impacted. In order for OEMs and users to protect their systems from failing, they must have a dependable sensor in place that can perform to the necessary standard. The natural question that arises from this is what must an engineer take into account when assessing and deciding on the sensor that best fits their system?

Industry standards have played a part in setting current expectations for sensor performance, functionality and reliability. It is important that engineers have an in-depth understanding of industry standards, as it means that they can then decide on a sensor that fits the system’s needs and that customer expectations are met. Industry standards are critical across a number of sectors - for instance transportation. This is because these requirements have an effect on sensor qualities when it comes to environmental sealing, noise immunity, temperature range and vibration. Each of these four standards can affect both a design engineer and an OEM.

Environmental sealing
Environmental sealing is concerned with a sensor’s ingress protection against water and dust while in operation. If engineers are to be as knowledgeable as possible, then they need to be aware of the Ingress Protection (IP) rating, which determines the level of protection provided against intrusion. The rating is published by the IEC (International Electrotechnical Commission). The highest rating a sensor can be awarded is IP69K. The first number is indicative of the sensor’s solid particle protection from a range of 0-6, with a rating of 6 meaning that the sensor is impervious to dust. The second number indicates the sensor’s water protection rating from a range of 0 to 9K. A 9K rating would mean that the sensor is water repellant with regard to close range high pressure, high temperature spray downs.

Let’s look at an example of how these standards can better inform engineers and ensure that they specify the most appropriate model. If an engineer has to decide on a sensor for heavy duty machinery, such as a combine harvester, they must consider the specific factors that the equipment must be protected against. A combine harvester would frequently be exposed to large amounts of dust and soil - not to mention water given the rigorous cleaning from a power washer it would be subjected to. Knowing IP ratings and their meanings would allow an engineer to specify a sensor that is suitably safeguarded against these issues.

Furthermore, engineers can turn to industry standards to avoid wasting time and effort designing further, unnecessary layers of protection. If an engineer is unaware that a sensor is 9K rated and consequently is as secure as can be, they might plan for additional o-rings to protect an excavator’s sensors against water exposure.

Electrical noise immunity
While the amount of electrical noise generated may sound inconsequential, the inverse is true. In fact, electrical noise immunity and Electromagnetic Compatibility (EMC) are at the higher end of industry standards in terms of importance, especially in today’s world. Our everyday devices are constantly becoming smarter and more connected. And as every mobile phone, radio tower, and wireless device releases electric noise, the amount of interference is becoming even more widespread.

There is no shortage of real life examples of electrical noise levels wreaking havoc on systems and causing sensor failures. An executive at a car manufacturer reported the engine of a prototype stalling as he was arriving at a local airport. Initially, the engineering team was at a loss to explain the reason behind this. However, after conducting a thorough investigation they found their explanation. Their tests revealed it was not coincidental that the engine stalling coincided with the executive taking a call on his mobile phone. The electrical noise emitted from the device and the noise from the airport caused the engine’s feedback loop sensor to fail, as noise immunity levels had been exceeded.

Clearly electrical noise is not an issue to be taken lightly, and can have a detrimental, even dangerous impact if not managed properly. To avoid reoccurrences of these incidents, engineers should consider noise immunity rating. A great number of sensors used in the automotive industry for example, have traditionally been rated at 60V per metre. However, the industry has recognised that changes need to be made to keep up with the times. Electrical noise immunity is not expected to lessen in the next few years, so it is essential that the number of volts per metre in sensors rises to accommodate this. Thankfully, the industry is moving towards ratings of 100-200V per meter.

It goes without saying that there are various industries which rely heavily on their machinery, and need it to be constantly available. A system failure on account of noise immunity can be particularly troublesome to find a solution. It can take engineers some time, which unfortunately can suspend business operations and revenue for longer than business owners would like. Knowing how noise immunity standards are expected to evolve over the coming years can help prevent system failures and minimise future damage.

Unlike environmental sealing, there isn’t one set body that regulates the temperature range for sensors – though there are industry norms that the majority of sensor manufacturers tend to follow. Most commercial products use sensors with a temperature range of -20 to +85°F. As long as the temperature falls between these two values, the sensor can operate without causing any damage to the equipment.

For certain industries, the same temperature range cannot be applied. One such example is the transportation industry, where the temperature range is -40 to +150°F. The greater range of values offers a higher level of protection against equipment failure, irrespective of the location the sensor is operating in. In certain parts of the world, like the Australian Outback, the sensor would need to be able to operate accurately and safely in a harsh environment. If a sensor is exposed to temperatures that fall out of the range, it can be damaged or its level of accuracy can fall.

In order to prevent an incident like this from happening, OEMs can design additional layers of protection for the sensor in much the same way that they would for environmental sealing. However, protecting the sensor from exposure to abnormal temperatures can be expensive and time consuming for design engineers. It is far more advantageous for a business to opt for an appropriate sensor in the first instance.

It may not seem as though vibrations possess the capability to cause a problem for sensors, but if they are not sturdy enough to handle constant vibrations the overall machine can be put at risk. Heavy machines frequently travel off-road and experience powerful vibrations for this reason. Vibrations are also caused by the large diesel engines used where sensors are in sub-systems such as hydraulic pumps, actuators and electric motors. The operator can receive false signals and the equipment can be damaged if a sensor is not able to remain unaffected by vibration conditions.

The two types of vibrations that engineers must be wary of are random vibration and high frequency vibration. Random vibrations are commonplace when a machine moves in off-road conditions, construction sites and other rough terrain. An important standard for these conditions is MIL-STD-202-214 Test Condition I, which is a product of the Department of Defense. A sensor that meets this standard can perform accurately in spite of any vibrations that may affect it, even if they come from the bottom or the side of the sensor.

High frequency vibration is a by-product of machines with large diesel engines. To be able to withstand this, sensors should meet the MIL-STD-202-204 Test Condition D standard, again established by the Department of Defense. A machine equipped with sensors that meet this standard can operate without being at risk of a sensor related failure, as the MIL-STD-202-204 Test Condition D standard is an extremely stringent one.

The number of smart machines and sensors in use continues to rise without any sign of slowing down. Engineers across numerous sectors will be under pressure to specify reliable and accurate sensors that can keep up with the demands placed by challenging conditions. The key to specifying the best possible sensor is having a detailed understanding of industry standards – and the best possible sensor translates into dependability and increased value for customers.

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