Review - Digital Thermometer
Digital Dual Two Channel 2 K-Type Thermometer
[Aug. 18, 2015]
[8/19/2-15 - additional thoughts]
This was purchased online for $16.30 (2014 pricing). The specific product name: AGPtek® Digital Dual Two Channel 2 K-Type Thermometer Thermocouple Sensor 1300 2372
I purchased this digital thermometer for use in the shop, initially for working with shrink fitting of small parts. Eventually, I hope to build a small propane furnace, and use the thermometer to monitor furnace temperatures.
Product Specifications
Per the vendor:
Description:
5 digits Large LCD display High Resolution up to 0.1 °C & 0.1 °F User Calibration of Temperature and Restore Factory Setting Low battery indication Data Hold function mode Maximum (MAX), Minimum (MIN) and Average Temperature Measurement (AVG) 2 channel temperature measurement (T1 & T2) Differential Temperature Measurement (T1 - T2) Extra 2 pieces of Metal Temperature Probes Switchable between °C, °F & °K Temperature range: -50 ~ 1300 °C (-58 ~ 2372 °F) Accuracy: 0.1 °C 0.4 Operating Temperature: 0 ~ 40 °C (32 ~ 104 °F) Operating Humidity: 0 ~ 70 % (R.H.) Celsius and Fahrenheit selectable Input protection: 60V DC or 24V AC maximum input voltage on any combination input pins Reading rate: 2.5 times per second Input connector: accept standard miniature thermocouple connectors Battery: standard 9V battery(included) Dimension:149x71x41mm(Approx.)
Package included:
1 x Digital thermometer 2 x Test probe 1 x English user manual
PS: The thermometer itself can sensor 1300, but the 2 test probes can only test the temperature up to 250 °C so if you need to test more than 250, please change these two probes.
Testing
Since I don't have an independent high temperature thermometer, all of my testing so far had been done on the assumption that the digital thermometer is giving accurate readings.
My first test was to check the temperature of a toaster oven I have been using for tempering metal. I found that the dial settings on the oven were fairly accurate.
My second test was to try the probe at much higher temperatures. Even though the vendor says the probes are only good up to 250 °C (482 °F), I decided to test one of the probes at metal hardening temperatures. (I should also note that high temperature probes can be purchased separately that will work with this digital thermometer). Per the Wikipedia article on thermocouples, type K thermocouples have a temperature range of −200 °C to +1350 °C (-330 °F to +2460 °F).
In order to test the probe, I made a metal "sleeve" by drilling a blind hole in a section of steel rod. The purpose of the sleeve is shield the probe from direct contact with the flame of the MAPP gas torch I used for testing (as I thought it unlikely that the probe would long survive direct flame contact). The picture below show the probe before and after testing; note that while a small section of heat shrink tubing (I assume) has completely burned away the woven cover and the probe itself do not appear to be damaged.
Probe and sleeve before testing.
Probe and sleeve after testing.
I ran five separate tests on the probe, heating it to the temperatures indicated in the table below.
The "time of test" is given to provide an idea of how much time elapsed between tests. The "hold time" is the time the probe was kept at the indicated temperature.
The photo to the left shows the sleeve and probe being heated with the MAPP torch, while sitting on firebrick.
The photo to the left shows the sleeve and probe at the end of Test #5 above, just after removal of the torch.
Conclusions
I am very satisfied with this purchase - a great bargain for the price. With respect to the idea of using the probes at temperature above 250 °C it is clear that, with some precautions, this is possible. However, it must be noted that the testing above was quite limited, so whether the probes will withstand extended use at very high temperatures is not known. Also, be aware that some minor damage (burning/melting of shrink wrap tubing) occurs at higher temperatures, but this does not adversely impact function.
In the event that the probes eventually succumb to higher temperatures, high temperature K type probes can be purchased to fit this unit, although based on a few quick online searches the high temperature sensors appear to cost more than the digital thermometer!
For use at higher temperatures, in a gas flame environment, a protective sleeve is probably a necessity. For this purpose. I plan to use stainless steel in the future. Use of a protective sleeve will increase the response time of the probe, but this should not be a problem for most practical uses (at least for use as a "furnace monitor").
For links to more information on heat treating, click on the link below and scroll down to "Heat Treating":
https://sites.google.com/site/lagadoacademy/useful-links#info-other