Generally, you can calibrate temperature sensors in a liquid bath or in a dry-block. This is also the case with the sanitary temperature sensors.
Let’s discuss next what these are and what are the main pros and cons of both.
Liquid bath
As the name suggests, a temperature liquid bath has liquid inside. The liquid is heated / cooled to the required temperature and the temperature sensors to be calibrated are inserted into the liquid. Often the liquid is stirred for even temperature in the liquid.
Liquid bath pros and cons
A liquid bath makes it easier to insert any shape of sensors in it and you can also use a reference probe inserted at the same time. Depending on the size of the liquid bath, you may insert several sensors to be calibrated at the same time. In case the sensor to be calibrated is an odd shape, a benefit is that it will still fit inside the liquid bath.
A liquid bath often enables better uniformity and accuracy than a dry-block due to better heat transfer of liquid.
So, this starts to sounds like a favorable option?
A liquid bath has anyhow several drawbacks as to why it is not always the best option:
A liquid bath always includes some sort of liquid, such as silicone oil, and often you don’t want to contaminate the sanitary sensor in such a liquid. There is a lot of cleaning after the calibration to ensure that the sensor is clean when installed back into the process.
Handling of hot oil is dangerous and any spills may cause injuries.
Any oil spills make the floor very slippery and can cause accidents.
Liquid baths are very slow. Even if it could fit several sensors in at the same time, it is often several times slower than a dry-block, so overall effectivity is not really any better. Sometimes people may have several baths, each set to different temperature, and they move the sensors manually between the baths to skip the waiting time of the bath to change temperature. This may work in a calibration laboratory but is naturally a very expensive way to calibrate.
The sanitary sensor should be placed so that the surface of the liquid touches the bottom of the flange, but in practice this is not always that easy to do. For example silicon oil has pretty large thermal expansion, it means that the surface level is changing slightly as the temperature changes. So, you may need to adjust the height of the sanitary sensor during the calibration. Also, due to the stirring of the liquid, there are small waves on the surface and the liquid level is often deep in the bath, so it is difficult to see that the sensor is at the right depth.
Liquid baths are often large, heavy and expensive equipment.
Dry-block
A temperature dry-block (or dry-well) is a device that can be heated and / or cooled to different temperature values, and as the name suggests, it is used dry, without any liquids.
Dry-block pros and cons
As the earlier chapter discussed the pro and cons of a liquid bath in this application, let’s look at the same also for the dry-block.
The main pros of calibrating the sanitary sensor in a dry-block include:
As it is a dry, it is also clean and does not contaminate the sanitary sensor to be calibrated. Sure, the sensor should still be cleaned after calibration, but the cleaning is way easier than with a liquid bath.
A dry-block is also a very fast to change temperature.
When using a dedicated insert with proper drillings, it is easy to insert the sanitary sensor always the same way (no adjustments), and the calibration is repeatable every time and with different users.
A dry-block is light and easy to carry compared to liquid bath.
Typically, a dry-block is also cheaper than a liquid bath.
On the downside, a dry-block is a less accurate than a liquid bath, it typically only calibrates one sanitary sensor at a time and needs different inserts drilled for different diameter sensors.
Despite these downsides, customers often prefer to make the calibration of their short sanitary sensors in a dry-block.
So, let’s discuss next the different considerations when calibrating in a dry-block.
