How is a thermometer an analog device


One knows the saying “many experts, many opinions” from everyday life only too well. When measuring the temperature with different measuring devices and measuring methods, differences can also occur that may make you wonder at first. As humans, we are inclined to initially place more trust in a digital device than an analog device. Is that justified? A finely scaled display in particular tempts us to get a sense of precision even more.

It is therefore important to explain what the terms measuring and display accuracy are all about and how the measuring devices commonly used in aquaristics, terrariums and garden ponds behave.

The display accuracy

The accuracy of the display with analogue thermometers can be recognized by the painted scale. In the hobby this is usual at intervals of 1 ° C. Thus the display accuracy is 1 ° C. Digital thermometers usually have a display accuracy of 0.1 ° C in which the measured value is displayed. The accuracy of the display has no influence on the accuracy of a measuring device, but only in the way in which the measured value obtained can be reproduced in detail.

The measurement accuracy

The measurement accuracy describes the precision of the thermometer. It means the correctness of the measured value taking into account the deviations due to the measuring method compared to the real physical measured value. In short, if the physical measured value is 25.0 ° C, how much deviation above and below this value are to be tolerated or the measurement result may deviate from it.

Practical examples

The digital thermometers JBL Aquarium Thermometers DigiScan and JBL Aquarium Thermometers DigiScan Alarm have a display accuracy of 0.1 ° C and a measurement accuracy of +/- 1 ° C with a display range of 0-40 ° C. In extreme cases, this can result in differences of 2 ° C between different measuring devices, since the deviation from the physical measured value, we assume 25 ° C for this, may vary from 24 to 26. Strict quality controls ensure that these deviations are not violated.

At this point we are making a comparison with a clinical thermometer to clarify the relationships. Clinical thermometers also have a display accuracy of 0.1 ° C. Measurement accuracy and the associated deviations for this sensitive area are a maximum of +/- 0.3 ° C for digital thermometers, which is defined in accordance with a DIN standard. Differences of up to 0.6 ° C are therefore considered to be okay. Depending on the measuring method, a deviation of 0.2-0.6 ° C (+/- 0.1-0.3 ° C measuring accuracy) is usual for devices available on the market. These devices measure in a very narrow temperature range of 35-42 ° C and thus only cover 7 ° C as a display range. Aquarium and terrarium thermometers measure between 0-40 ° C (sometimes up to 50 ° C) and thus cover 5.7 and 7.1 times the range. If you put this in relation to the measurement accuracy, even a clinical thermometer would not have a measurement accuracy of +/- 1 ° C, but rather +/- 1.15 ° C on average (max: +/- 1.74 & min: + / - 0.57 ° C). A very high measurement accuracy is only possible with methods that measure in a very narrow temperature range. High measurement accuracies are nevertheless achieved in the large temperature ranges mentioned.

Impact & Findings

The combination of the measurement accuracy and the display accuracy can result in a deviation from the true value of the physical quantity. This affects every measuring device and is within an acceptable framework for the respective area of ​​application and is therefore less important, as it would not lead to a different recommendation for action or evaluation. Our feeling always demands exactly congruent measured values ​​and in the finest scaling steps. Once we are honest with ourselves, the deviations do not mean a change in judgment or recommendations for our animals. With a clinical thermometer or standard room thermometers, you will also encounter deviations that you have probably not stumbled upon before.

It is more important that the measurement is carried out correctly. In the aquarium and pond, for example, there is not always an even mixture, so that the temperature near the heater can be higher than at the other end. Therefore, heaters should always be installed at a water point with a good flow. In the terrarium, the temperature differences occur intentionally, so that animals can move in a targeted manner in a sun and shadow area. Therefore, pay close attention to your measurement location and choose it carefully. A second measurement often provides the necessary clarity.

Overview of the display and measurement accuracy

In the following overview we have compiled all JBL products with their measurement and display accuracy. Feel free to compare these with other manufacturers. You will find that you will not find any precise products in this price segment.

Display accuracyMeasurement accuracy
JBL PROFLORA pH-Control Touch0.1 ° C+/- 0.4 ° C
JBL CoolControl2.0 ° C+/- 1.5 ° C
JBL PROTEMP S 1000.5 ° C+/- 1.0 ° C
JBL Aquarium Thermometer Slim1.0 ° C+/- 1.5 ° C
JBL Aquariium thermometer hang-on1.0 ° C+/- 1.5 ° C
JBL Aquarium Thermometer DigiScan Alarm0.1 ° C+/- 1.0 ° C
JBL Aquarium Thermometer DigiScan0.1 ° C+/- 1.0 ° C
JBL aquarium thermometer digital2.0 ° C+/- 2.0 ° C
JBL Aquarium Thermometer Mini1.0 ° C+/- 1.5 ° C
JBL Aquarium Thermometer Float1.0 ° C+/- 1.5 ° C
JBL hydrometers1.0 ° C+/- 1.5 ° C

background knowledge

Finally, we will give you a few more facts about the measuring methods used by JBL.

In the aquarium hobby, analog thermometers are usually expansion thermometers, in which an alcoholic solution with dye rises over expansion on a glass capillary. Mercury and other toxic substances are not used here, so that your fish are not in danger even if they break. Only the glass splinters should be vacuumed. These thermometers are 100% waterproof and do not require electricity. They are easy to clean and disinfect. There is also no risk of an allergic reaction to the user from nickel or other metals.

Digital thermometers in aquaristics and terraristics either have a measuring probe with a cable or a contact point directly on the underside of the display device. These measure the temperature on the surface of the sensor via a sensor point. With some devices this is immersed directly into the water, with others the superficial contact with the aquarium pane is used.

Infrared thermometers, which measure the temperature on a surface, can be used in terraristics, where, for example, stones or the substrate can be measured. This method is useless in the aquarium hobby because reflections on the water surface lead to enormous deviations.