DT890B digital multimeter to measure temperature

DT890B digital multimeter to measure temperature

The 23rd issue of "Electronics News" in 2005 published an article entitled "Adding Temperature Measurement Function to Digital Multimeters". Later, in the 45th issue of the same year, an article questioning the article was published, and an improvement method was proposed. In fact, the so-called improvement is nothing more than the normal use of LM35DE. The original intention of the former is to use the power supply inside the meter with the probe to complete the measurement without an external power supply, but as the latter said, this circuit does not work at all. Is it really impossible without an external power supply? After many experiments by the author, the circuit shown in the attached figure achieved the purpose. After comparing the measured values ​​with the values ​​measured by the external power supply method, the error is extremely small. Only when the 9V voltage is lower than 8V does a larger error appear. The production method is as follows:

Connect a two-core shielded wire to the LM35DE, insulate the solder joint with a heat shrink tube, and then insert it into a hollowed-out aluminum electrolytic capacitor. Use hot melt adhesive to seal it. Solder a φ3.5mm stereo plug on the other end, and the probe is ready.

The next step is to drill a hole in the lower right corner of the multimeter, install the φ3.5mm socket, lead out the three wires and connect them to their respective positions, and you're done.