Thermometers are high-precision measuring instruments

No doubt everyone is familiar with those simple thermometers with a measuring scale and a green, blue or red line in the centre. This changes depending on the temperature. The liquid that forms this line expands when heated and contracts again when cooled. So it rises as soon as it gets warmer and falls when it cools down again. Reading the values, however, is often quite inaccurate and barely possible by tenths. The digital thermometer, on the other hand, has a sensor on the front tip of the probe. There are various types of sensor which can be selected for the respective measuring task.

The measurement of temperatures using thermocouples is based on the thermoelectric effect. If two legs made of different metal alloys are welded at their ends, an electrical current flows when the measuring point (hot end) has a different temperature from the cold junction (cold end). Each thermocouple material has its own characteristic curve. The characteristic curve shows the relationship between the temperature applied and the electrical voltage generated. In practice, Testo customer groups mainly use type K thermocouples in industry and air conditioning technology and type T thermocouples in the food sector.

Platinum resistance sensors are based on the so-called PTC resistor effect. All metals are for instance positors, as they have the characteristic of increasing their electrical resistance when the temperature rises (i.e. they conduct current better when cold than when hot). This effect can be used to measure temperatures. Probes with platinum resistance sensors are among the most accurate sensors available. They are durable and resistant to ageing. They are above all used in the laboratory sector.

Thermistors (or NTCs) are modern temperature sensors which convert temperature changes into resistance changes. In contrast to the platinum resistance sensors which have just been presented, their resistance falls as the temperature rises. Because they have a negative temperature coefficient, they are also known as NTCs. Thermometers with NTC technology do not need any time to acclimatize to the ambient temperature (because they do not have any cold junction). This makes them ideal for use in refrigerated and deep-freeze rooms.

Advantages of digital thermometers are:

• Ultimate measuring accuracy
• Reliable temperature measurement in the respective medium
• Accurate measurement in tenths and even hundredths
• Robust workmanship
• Data storage possible

But a digital thermometer has another advantage. It can be used in conjunction with a temperature data logger and thus enables the collection and storage of temperature data. These values are required over an extended period of time, for example when testing refrigeration appliances or air conditioning systems. The stored data can also be used to prove compliance with a consistent temperature in a food chain.

Testo offers the right thermometer for every need. Whether you are looking for a digital thermometer to use in your home and garden, or whether it needs to be a high-performance instrument to support you in your business, such as a member of the Smart Probes: in all sectors, thermometers are among the most frequently used measuring instruments. All of the variants are impressive thanks to their reliable temperature measurement. The meat thermometer is used in the home as well as in gastronomy. Used in the form of a penetration thermometer, this ensures that the cook knows the core temperature of the food to be prepared. Since this can check not only meat, but also fish and other foods, this thermometer is also called a roasting thermometer.