“Relative humidity makes your hair go frizzy on a cold day,” says Jeremy Wingate, head of sales at industry tool manufacturer Rotronic Instruments UK.
“It is how much gaseous water is in the air compared to how much there could be; how close the air is to being saturated.”
When you get to 100% relative humidity, you get visible effects such as condensation on a window, dew on the grass, a cloud above a kettle. Anything below 100%, you can’t see. But you will notice its effects – and not just on your hair.
“Every industry has someone measuring relative humidity. One day I’ll go to a car manufacturer, the next to a power plant,” says Wingate.
Industry 4.0 measures everything live, including relative humidity, and sees what is going wrong before it is seen by the customer. We can then do planned maintenance which is less disruptive and expensive
Jeremy Wingate, head of sales, Rotronic Instruments UK
Vincent Hess, senior product manager for humidity sensors at Switzerland headquartered product maker Sensirion, says humidity can impact products and processes in various ways.
“Humidity has a large influence on corrosion, while certain goods are sensitive to humidity, such as fresh food or pharmaceuticals.”
Humidity cannot be removed, of course, merely adjusted, and indeed many production lines require it to be at particular levels, not just to avoid problems, but to create required conditions.
“Certain processes, such as combustion, depend on humidity,” says Hess. “The air taken into combustion engines is measured for humidity, and the information is used to optimise that process.”
Whatever you are manufacturing, an understanding of relative humidity levels is important, and process plants have measured the variable for some time.
As a result of over 40 years of continuous development, the sensor has evolved significantly from the first generation
Jarkko Ruonala, product manager, Vaisala Industrial Measurements
Jarkko Ruonala, product manager at Finland-based Vaisala Industrial Measurements, says historical methods included observation of thermodynamic parameters – such as by calculating the temperature change required to cause condensation or evaporation.
Capacitive sensors were introduced in the 1980s, Ruonala says. His company makes the Humicap relative humidity and temperature probe which is typically used in industrial drying kilns and baking ovens, among other applications.
“The first Humicaps were developed for the needs of weather balloons, where the measurement has to be fast and withstand rough conditions such as high humidity when travelling through the clouds,” says Ruonala.
“As a result of over 40 years of continuous development, the sensor has evolved significantly from the first generation.”
The Humicap sensor consists of a very thin specially engineered polymer layer between two conductive electrodes, one of which allows free diffusion of water vapour in and out of the polymer.
“Electrically, the sensor creates a capacitor, which changes its capacitance when the active polymer equilibrates with the ambient humidity.”
Hess says humidity sensors have become much cheaper and more user friendly since becoming available in a pre-calibrated form at the start of this century.
“Our first product in 2002 was already calibrated, you could reflow solder it, and you had a digital signal. The main benefit was ease of integration, you did not need humidity measurement capabilities to build an accurate product.”
As with most products in use today, humidity sensors have shrunk in recent times. “Our product is as small as 1 mm2 by 0.5 mm height; and more functionality is integrated – a single chip includes the sensor and the electronic circuitry.”
Sensirion sensors have I2c digital signal outputs. “They can be read by any microcontroller, which are in almost all electronic devices. If you have the sensor, a microcontroller, some memory and wireless chip, then you can transfer the data to the Cloud and then people can view it on their personal devices.”
The firm’s SHT3X range is best suited to process applications, according to Hess. “The sensors still measure humidity and temperature but they are more accurate than 15 years ago over a wide range of operating conditions; long-term stability is improved, power consumption has come down and prices have reduced.”
This all means humidity sensors can be used in more places on more production lines. “The biggest difference is that affordability leads to a higher abundance of sensors, so you have more data you can use.”
Wingate says the collection – and use of – information is the latest big change in the measurement of relative humidity.
“The massive shift is data,” he says. “Ten years ago, if a pharmaceuticals manufacturer needed to measure humidity in a powder blending room, they would stick a calibrated sensor in there and put an analogue signal into some hardware that would control the dry air.”
Movement towards the fabled Industry 4.0 has changed all this. “Now we are looking at pulling data in and measuring other parameters all in one place to create a central brain that sees what’s happening, has seen similar events before and can raise warnings.”
This development aims to spot humidity changes before they cause a problem. “If a process is failing then an engineer can spend half a day looking at it, not have the right parts and have to come back another time,” says Wingate.
The sensors still measure humidity and temperature but they are more accurate than 15 years ago over a wide range of operating conditions; long-term stability is improved, power consumption has come down and prices have reduced
Vincent Hess, senior product manager, Sensirion
“Industry 4.0 measures everything live, including relative humidity, and sees what is going wrong before it is seen by the customer. We can then do planned maintenance which is less disruptive and expensive.”
The idea is that relative humidity is not seen in isolation but as part of a bigger picture, through a system such as Rotronic’s RMS data recording system, which can be accessed through personal devices.
“Manufacturers can see live data on their phone rather than having to log in to a screen in the same building,” says Wingate.
“Traditionally you would have basic nuggets and you might download it at the end of the week when it’s too late and you can’t sell a batch you’ve made. Now you know data live so you can react quicker.”
The integrated system is designed to help process plant bosses piece together a picture more quickly.
“You may see a dodgy relative humidity reading then see that the plant processing system is offline and it is shutdown day. With the old system you would have emails saying relative humidity has gone wrong, now you can see that the plant isn’t being used.”
Catching the ‘bus’
Ruonala says ‘field bus’ technology, where multiple instruments are integrated, is becoming more popular for sensor-based measurement in manufacturing.
“Various field bus technologies are now increasing their popularity, as they allow an increase in the amount of data that be transferred in addition to the actual measurement signal,” he says.
Flexibility of a measurement system for transferring data between systems, and the ability to meet different needs, is more important than ever, says Ruonala.
“The Internet of Things and the whole new paradigm in industrial automation are changing the industry. This revolution of data use is still in the beginning but is picking up speed all the time.”
Hess believes technology will continue to make use of sensors cheaper and more beneficial, allowing relative humidity to be measured in more parts of a process, and potentially expanding the ways the data is used.
“Currently either you can control humidity or control other areas of the process to cope better with the humidity level you know,” he says.
But as well as using data to see where humidity is a sign of a process failing, it could also highlight where the process could be close to failing due to humidity levels.
“I think there could be a number of processes where humidity has an influence on how long equipment works. So far this is not really being addressed,” says Hess. “We could see humidity sensors used more to help.”