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A Guide To Level & Pressure Measurement In Harsh Conditions

caustic wastewater in the arcticLike a jigsaw puzzle, harsh conditions can excite an eager engineer or control tech. They’re difficult, which only makes them more rewarding to solve. However, they can also be a headache, a thorn in your side.

Design engineers who work with instrumentation are equally intrigued and excited about a good challenge. Some of them become even more versed in the fine details of a harsh condition than the expert in the field once they get the details and begin to recreate the scenario.

Through a lot of R&D, we have a myriad of sensors that pretty well cover the gamut of harsh conditions. So, as an ode to the challenging puzzle that is harsh conditions, we discuss the ins and outs of the harsh.

Defining Harsh

In a subjective world, certain words have a difficult time getting the point across. Harsh is one of those words. It means something totally different to the oil and gas engineer than to the process engineer.

For this post, we’ll keep it simple and allow subjectivity. Harsh means there is something about the environment, man-made or otherwise, that makes the measurement difficult compared to other application variables.

Harsh does not mean unsolvable. There are plenty of very difficult circumstances that have been solved by the proper application of sensors and other technology. Harsh also doesn’t mean expensive. Almost anybody with experience in with measurement and control of liquids can point to examples where a $3,000 radar sensor failed while a $300 pressure transmitter excelled.

That said, we’ll cover the following harsh conditions:

  • Dirt & Dust
  • Moisture & Water
  • Caustic Chemicals
  • Temperature
  • Vibration & Shock
  • Flammable Vapors

Dirt & Dust

Dirt and dust are headaches for electronic devices. If they creep their way into circuit boards or build up on electrical connections they can render a sensor useless. This is why it is important to seek out sensors with adequate protection if dust is present in your application. Look for NEMA and IP ratings, which both include codes that represent the level of ingress protection a particular product has to dust and water.

For example, IP ratings typically have 2 numbers. The first number indicates the protection against solid objects while the second number indicates the protection against liquids. For the first number there are a total of 7 possible numbers (0-6); the higher the number, the better the protection against solids. 0 equals no protection while 6 equals total protection against dust.

Our PG7 and PG10 digital pressure gauge models have IP ratings that start with a 6, meaning they are totally protected against dust.

Moisture & Water

Have you ever dropped a mobile phone in a puddle? Or put your MP3 player through the washing machine? If you have, you are familiar with the damage moisture can cause to electronics. Most consumer electronics won’t survive being submerged in water but many industrial sensors are designed for that very purpose.

Again, ingress protection ratings such as NEMA and IP will help you determine how a sensor handles moisture.

For IP ratings look at the second number. There are a total of 9 possible numbers (0-8) with 0 being no protection and 8 being the highest level of protection against liquids.

As mentioned earlier, we have digital pressure gauge models with IP ratings. While they both have the same first number (6 for total dust protection), they have different second numbers. For example, our PG10 has an IP rating of IP 65. This means that it is totally protected against dust and protected against low pressure jets of water from all directions. On the other hand, our PG7 has an IP 67 rating. The 7 means that the PG7 can be submerged in water to a depth of 1 meter with no effect on performance.

There are also sensors designed for submersion in liquids at great depth called submersible pressure transducers. For example, ours is rated IP68 and can work at depths up to 450 ft.

Caustic Chemicals

Caustic chemicals need to be measured and monitored too. But not all sensors are up to the job.

Some chemicals react with certain materials and not with others. This is why you need to have a good understanding of the chemical you are dealing with. Take a look at the MSDS sheet to see of what the chemical is made. Quite often, chemical compatibility information is listed letting you know which materials to avoid.

Also know what the material your sensor is made out of and which parts of the sensor the chemical will be or might be touching.

Here at APG we offer sensors made out of a variety of materials. Many of our pressure transducers are made out of 316L SS, a steel grade known for high chemical compatibility. Many of our ultrasonic sensors have Kynar (PVDF) faced transducers another material known for compatibility with a large number of chemicals.

Temperature

If electronics get too hot or too cold they will fail. Some sensors are made out of electrical components that just won’t work once a certain temperature is reached. This could be due to adhesives breaking down if temperatures are too high, or components becoming brittle and prone to breakage due to cold temperatures. This is why it is important to study the spec sheet for the particular product you are considering. Most sensor manufacturers list temperature ratings detailing the limits their product.

Be aware of the different type of temperature ratings and what they mean. Most manufacturers will list up to 3 different types of temperature ranges: compensated, operating, and storage.

Compensated temperature range is the range at which a sensor will still maintain its rated accuracy. Meanwhile, the operating temperature range lets you know at which temperatures the sensor will still function. So, if your sensor is currently operating at a temperature outside of the compensated range, but within the operating range, know that the accuracy of your readings may be out of spec.

Finally, the storage temperature range is the range at which a sensor can be stored but still function properly once the unit is installed. In some cases this means that while you may be free to store the sensor in extreme temperature conditions, don’t expect it to work in those same conditions.

Vibration & Shock

Whether it’s from pumps or other equipment, vibration from machinery can quickly destroy a sensor not fit for the job.

We sell a variety of sensors into the oilfield where vibration and even collision are expected. For these types of sensors, we sell them with heavy duty housings, full potting of the boards, and laser welded assemblies.

In applications where a display is desired we have often recommended that the pressure transducer be tethered to the gauge by a cable. This allows the user to mount the display part of the unit away from the vibration.

Talk with your sensor supplier if you are concerned about shock and vibration to ensure that necessary steps are taken in the build of the product to adequately deal with it.

Flammable Vapors

Last but certainly not least is to make sure your sensor is certified to work in hazardous locations if flammable gasses are present. Rather than the risk of losing a sensor, safety for personnel is the concern here. Make sure you understand the type of hazards that are present at your application to determine which type of class or division/zone approvals you will need for the measurement device.

The world of class and division/zone approvals for hazardous locations is large and can often be overwhelming at times but understanding the basics can help.

To keep things simple, remember the following: Sensors that are approved for use in environments with flammable vapors will need to have a Class 1 approval. Then, depending on how often you can expect the hazardous gas to be present determines what the division or zone needs to be:

  1. If the hazard will be present at all times then you need a device approved for Zone 0 or Division 1.
  2. If the hazard is expected to be present under normal conditions then you need a device approved for Zone 1 or Division 1.
  3. If the hazard is expected to only be present in abnormal conditions then you need a device approved for Zone 2 or Division 2.

If you have any questions on these approvals, be sure to work with your manufacturer and any other resources available to you.

Please reach out to us if you would like assistance with picking the right sensor to work in harsh conditions. We are always happy to help.


Scared of level measurement in harsh conditions? Well don't be! Learn more about why continuous float level transmitters can take what you have to throw at them below:

continuous float level transmitters for harsh conditions

top photo credit: Eli Duke via flickr cc

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