Independent sensors ?

We at ICU Scandinavia often talk about the importance of using independent (or parallel) sensors for monitoring and log, what we mean is that there are certain risks associated with us relying on the equipment’s built-in sensors and its display.

Perhaps we find the clearest and simplest example at home, in the kitchen where the refrigerator display shows a temperature. But when you open the door and leave it open for a while, the display will remain the same temperature. The question is then of course: Is it still the same temperature inside the refrigerator or the display shows an incorrect temperature?

However, it is not as simple as it may look. We usually do not know where the built-in sensor is located. It may be hidden in the back of the cabinet or the installed in the front near the door, is it mounted high or low?        Or perhaps, the display might not show the current temperature at all …. but only the pre-set (desired) temperature?

You should also think about the refrigerator’s own temperature control (regulation), which is a closed system constantly striving to maintain the temperature at the pre-set value. Ie. if the built-in sensor for some reason starts to deviate or malfunction (eg shows +4°C when it is actually +6°C), the refrigerator temperature control never will notice or pay attention to it. As well as the refrigerator’s display will show +4°C when it is actually +6°C.

These simple examples thus show that we need to make a risk assessment if we want to have full traceability of our monitoring and log.

If you introduce independent sensors for logging, sensor that are completely decoupled from the refrigerator temperature control, you will have full control on your temperature logs:

• A temperature sensor only records the temperature at exactly the place where it is installed, therefore the positioning of the sensor is of great importance. What and where do you want to measure? (In the warmest place in the cabinet or the coldest, perhaps some sort of compromise or average position …. You decide.)
• A sensor mounted in the air, will always register air temperature …. but you are perhaps more interested in the core temperature? You can simulate (emulate) that by placing the sensor in a container of liquid or perhaps in a stabilization adapter (a body with a certain mass that the sensor may be fixed inside)
• A sensor must be calibrated regularly to ensure that it still shows the correct temperature. An independent / parallel sensor can be calibrated.

The above mentioned examples with refrigerator temperatures is of course applicable to other sensors and other devices as well; e.g. temperatures in freezers, CO2 or humidity in incubators, air pressure and flow in clean rooms etc.