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A thermocouple thermometer is a useful tool for every hobby lab. You can use it to measure the temperature of all components. We bought and examined the UT320A from UNI-T with a range of -40 °C to +260 °C. |
Introduction to the UT320A from UNI-T
Ideal for the electronics hobbyist
The UT320A is a temperature meter which works according to the thermocouple principle. The handy thing about a thermocouple temperature meter is that the actual measuring point is very small, namely the weld between two wires made of different metal alloys. With this small sensitive point you can measure for example the temperature of a transistor, without the thermal mass of the measuring probe affecting the temperature of the component.
A clarification of the measurement range
In most advertisements, a measuring range of -50 °C to +1,300 °C is specified. Why do we write -40 °C to +260 °C? Because the range of such a meter does not depend on the range that the meter can measure, but on the range that the supplied thermocouple can handle. As the thermocouple supplied with the UT320A can only measure between the last two temperatures mentioned, we consider this to be the range of this package.
If you want to measure higher temperatures you can do so with the UT320A, but then you have to buy another thermocouple that can handle this higher temperature.
Price and scope of delivery
The UT320A is available for a price ranging from $ 9.00 (Alibaba) to € 22.95 (Soldeershop). We ordered our specimen for € 18.39 from Grandado, who sends the order to a Chinese supplier, so the delivery time is quite long.
The thermocouple meter is delivered in a nice cardboard box. This contains the meter, a type-K thermocouple and a short, but clear English manual. Although some sales sites give the impression that the three necessary type AAA batteries are included, this is not the case.
The UT320A thermocouple meter
The meter itself is housed in a sturdy plastic case of 120 mm by 53 mm by 28 mm and weighs 116 grams, including the three batteries. The monochrome LCD display measures 32 mm by 35 mm, the digit height is 17 mm. It is a pity that the meter does not have a folding backrest. This means that the meter can only be laid flat on the table, which does not help its readability.
The technical data of the UT320A
According to the manufacturer, this temperature meter meets the following specifications:
- Measuring range: -50 °C to +1,300 °C
- Resolution: 0.1 °C
- Accuracy -50 °C to 0 °C: ±1.8 °C
- Accuracy 0 °C to +1,000 °C: ±[0.5 % + 1 °C]
- Accuracy +1,000 °C to +1,300 °C: ±[0.8 % + 1 °C]
- Sampling: four measurements per second
- Usable thermocouples: Type-K, Type-J
- Available thermocouples: UT-T01, UT-T03, UT-T04, UT-T05, UT-T06, UT-T07
- Supplied Thermocouple: UT-T01
- Power supply: 3 x 1,5 V type AAA battery
Please note that although the UT320A can measure up to +1,300 °C, the practical usable temperature range depends entirely on the thermocouple used!
The UT-T01 thermocouple: -40 °C to +260 °C
With the supplied type-K thermocouple UT-T01 you can measure only up to +260 °C. This is of course more than enough for the use in the electronics lab.
According to the manual, this thermocouple is only suitable for measuring on solid objects and not in liquids. However, we cannot discover why this should be so. Compared to other thermocouples in our possession that are suitable for measuring in liquids, we see no difference in the design of the tip of the thermocouple.
The wire of the thermocouple is 95 cm long and is only 1.0 mm thick. The connector is the well-known TE1260 mini thermocouple connector which has a narrow and a wide pin. In this way you can never connect the thermocouple incorrectly to the meter.
What is very good about this thermocouple is the extremely fine and small weld, only 1 mm in diameter, see the inset in the picture below. With such a tip you can even measure the temperature of an SMD part. Of course, you have to use a very small amount of heat-conducting paste with each measurement!
Concerning the accuracy of the UT-T01, UNI-T contradicts itself. In the manual of the UT320A an accuracy of ±2,0 °C is given. However, on the manufacturer's site an accuracy of ±0,75 % is mentioned.
The electronics in the UT320A
After removing four screws, you can open the case and get an idea of the internal electronics. As the picture below shows, it looks very neat. On the lower part of the PCB you can see the two large rectangular pads that supply the battery voltage via the contacts of the battery holder. In the black part of the housing is a small PCB perpendicular to the main PCB. The connector for the thermocouple and an NTC resistor are mounted on this. The latter is probably used to measure the connector's own temperature, so that the processor can calculate the cold junction compensation. Both boards are connected with solid solder joints.
The LCD display
The figure below shows which messages appear on the display in the various measuring modes. From this picture it is clear what you can do with the UT320A. The battery status icon only appears on the display when you need to replace the batteries.
The function of the four push buttons
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A clarification of the measurement range
In most advertisements, a measuring range of -50 °C to +1,300 °C is specified. Why do we write -40 °C to +260 °C? Because the range of such a meter does not depend on the range that the meter can measure, but on the range that the supplied thermocouple can handle. As the thermocouple supplied with the UT320A can only measure between the last two temperatures mentioned, we consider this to be the range of this package.
If you want to measure higher temperatures you can do so with the UT320A, but then you have to buy another thermocouple that can handle this higher temperature.
Price and scope of delivery
The UT320A is available for a price ranging from $ 9.00 (Alibaba) to € 22.95 (Soldeershop). We ordered our specimen for € 18.39 from Grandado, who sends the order to a Chinese supplier, so the delivery time is quite long.
The thermocouple meter is delivered in a nice cardboard box. This contains the meter, a type-K thermocouple and a short, but clear English manual. Although some sales sites give the impression that the three necessary type AAA batteries are included, this is not the case.
 |
| The scope of delivery of the UT320A. (© 2021 Jos Verstraten) |
The UT320A thermocouple meter
The meter itself is housed in a sturdy plastic case of 120 mm by 53 mm by 28 mm and weighs 116 grams, including the three batteries. The monochrome LCD display measures 32 mm by 35 mm, the digit height is 17 mm. It is a pity that the meter does not have a folding backrest. This means that the meter can only be laid flat on the table, which does not help its readability.
 |
| The four views of the UT320A. (© 2021 Jos Verstraten) |
The technical data of the UT320A
According to the manufacturer, this temperature meter meets the following specifications:
- Measuring range: -50 °C to +1,300 °C
- Resolution: 0.1 °C
- Accuracy -50 °C to 0 °C: ±1.8 °C
- Accuracy 0 °C to +1,000 °C: ±[0.5 % + 1 °C]
- Accuracy +1,000 °C to +1,300 °C: ±[0.8 % + 1 °C]
- Sampling: four measurements per second
- Usable thermocouples: Type-K, Type-J
- Available thermocouples: UT-T01, UT-T03, UT-T04, UT-T05, UT-T06, UT-T07
- Supplied Thermocouple: UT-T01
- Power supply: 3 x 1,5 V type AAA battery
Please note that although the UT320A can measure up to +1,300 °C, the practical usable temperature range depends entirely on the thermocouple used!
 |
| Other usable thermocouples of the UT-T0x series. (© 2021 Jos Verstraten) |
The UT-T01 thermocouple: -40 °C to +260 °C
With the supplied type-K thermocouple UT-T01 you can measure only up to +260 °C. This is of course more than enough for the use in the electronics lab.
According to the manual, this thermocouple is only suitable for measuring on solid objects and not in liquids. However, we cannot discover why this should be so. Compared to other thermocouples in our possession that are suitable for measuring in liquids, we see no difference in the design of the tip of the thermocouple.
The wire of the thermocouple is 95 cm long and is only 1.0 mm thick. The connector is the well-known TE1260 mini thermocouple connector which has a narrow and a wide pin. In this way you can never connect the thermocouple incorrectly to the meter.
What is very good about this thermocouple is the extremely fine and small weld, only 1 mm in diameter, see the inset in the picture below. With such a tip you can even measure the temperature of an SMD part. Of course, you have to use a very small amount of heat-conducting paste with each measurement!
Concerning the accuracy of the UT-T01, UNI-T contradicts itself. In the manual of the UT320A an accuracy of ±2,0 °C is given. However, on the manufacturer's site an accuracy of ±0,75 % is mentioned.
 |
| The supplied thermocouple UT-T01. (© 2021 Jos Verstraten) |
The electronics in the UT320A
After removing four screws, you can open the case and get an idea of the internal electronics. As the picture below shows, it looks very neat. On the lower part of the PCB you can see the two large rectangular pads that supply the battery voltage via the contacts of the battery holder. In the black part of the housing is a small PCB perpendicular to the main PCB. The connector for the thermocouple and an NTC resistor are mounted on this. The latter is probably used to measure the connector's own temperature, so that the processor can calculate the cold junction compensation. Both boards are connected with solid solder joints.
 |
| The internal of the UT320A. (© 2021 Jos Verstraten) |
Working with the UT320A
The LCD display
The figure below shows which messages appear on the display in the various measuring modes. From this picture it is clear what you can do with the UT320A. The battery status icon only appears on the display when you need to replace the batteries.
 |
| The indications on the display. (© 2021 Jos Verstraten) |
The function of the four push buttons
- Top left: ON/OFF
A short press switches the meter on or off. The display shows the icon for automatic switch off. After a few minutes the device will switch itself off. If you do not want this, press this button longer. This icon will then disappear from the display. - Top right: °C/°F
The selection of the unit of measurement, degrees celsius or degrees fahrenheit. - Bottom left: MODE
By pressing this button several times briefly, the meter will cycle through its four measuring modes. After one press the UT320A displays the maximum value measured in the measurement cycle. After the second press the minimum measured value is displayed. After the third press the meter calculates the average value of all measurements in the measuring cycle. Press again and the device again records the current temperature of the thermocouple junction. A longer press switches the thermometer between type-K and type-J thermocouple. - Bottom right: HOLD/BL
A short press on this button saves the current temperature on the display (DATA HOLD), a second short press reads the current temperature again. A longer press switches the display illumination on or off. This works very nicely, the whole display gets an uniform backlight that is not bright, but just good enough to read the display even in absolute darkness.
The UT320A in practice
This thermocouple meter is easy to use and to handle. However, you should be aware that it takes a few minutes after switching on the meter, or after plugging in the thermocouple, before the reading is stable. This has to do with the cold junction compensation which apparently has a certain adjustment time.
Unfortunately no accuracy test
Unfortunately, we cannot test the accuracy of the UT320A. We have no reference meter that is at least a factor of ten more accurate than this meter. The only thing we can do is to buy a bottle of distilled water, first cool the content until it contains ice and then heat it until it boils. As we know, these are the two calibration points of the Celsius scale. We will leave the influence of air pressure aside for the moment, as it is unimportant at this level of accuracy. At these two calibration points, our UT320A gives the following results:
- Freezing water: +1.3 °C
- Boiling water: +99.6 °C
If you consider that you are dealing with two accuracies, the accuracy of the meter and the accuracy of the thermocouple, then these results are satisfactory.
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