Different Temperature Sensors - Thermocouples, Thermistors, RTDs
Pharmaceutical companies make use of different temperature sensors due to their accuracy. Currently three sensors are widely used in the industry. Below is a brief on the three sensors.
Thermocouple
Thermocouple is the most commonly used temperature sensor; not only does the sensor provide high accuracy rate; it is also the least expensive of the three sensors. Aside from these, the sensor also has a broad operating range. The sensor has two metal conductors that are joined at the end. If the conductors are exposed to different temperatures, a thermal EMF is produced in the circuit. One junction is kept at a cold temperature and serves as the reference temperature level. The EMF result depends on the difference between the two junctions and is used to determine the temperature. The sensor can measure a wide range of temperatures, from -200 up to 2000C.
To protect the sensor from outside temperature or conditions, it is covered with metal or Teflon.
| Thermocouple Type | Conductors-Positive | Conductors-Negative |
|---|---|---|
| B | Platinum-30% rhodium | Platinum-6% rhodium |
| E | Nickel-chromium alloy | Copper-nickel alloy |
| J | Iron | Copper-nickel alloy |
| K | Nickel-chromium alloy | Nickel-aliminum alloy |
| N | Nickel-chromium-silicon alloy | Nickel-silicon-magnesium alloy |
| R | Platinum-13% rhodium | Platinum |
| S | Platinum-10% rhodium | Platinum |
| T | Copper | Copper-nickel alloy |
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RTD – Resistive Temperature Detectors
The RTD works on the premise of change in the resistance of the metal when a temperature change occurs. As the temperature increases, the metal resistance also increases and decreasing temperatures or cooling will decrease the resistance level. To determine the resistance level, a constant current is passed through the sensor at a different temperature level. The RTDs are made from platinum or nickel material.
Typical RTD (Resistive Temperature Dector)
Thermistor
Made of nickel cobalt or manganese, the Thermistor is also one of the common sensors available in the industry today. The sensor is small and often used for small devices such as TV or phones. Although it is smaller and has a small temperature range, it has a very high accuracy rate. This sensor is ideal for those who are looking for a fast response to the changes in the temperature level.
When Would You Use Them?
There are a number of points at which you might want to use temperature sensors. The first might be on any machinery you are using such as a Tablet / Pill Press or an Industrial Powder Mixer. Excessive heat detected here could be an indication that the machine is under too much pressure or that there is a fault that needs to be investigated.
You may also want to use it during the mixing process. Some compounds when coming together can cause an exothermic reaction. The heat generated from this reaction can damage the API or the properties of the excipients. If you are able to monitor the temperature you can see if it goes past the denaturing point.