# Digital temperature meter probe wire length

I bought a cheap Chinese digital thermometer like this one

with this description Link to product

Item specifics

Power Type: Button Battery
Model Number: Thermometer
Max Measuring Temperature: 50°C - 69°C
Style: Handheld
Theory: Temperature Controller
Display Size: 2.0 - 3.9 Inches
Display Type: Digital
Usage: Indoor


Product Description

Feature:

100% brand new and high quality.
Quantity: 1
Measuring temperature range: -50Celsius~110Celsius
Temperature accuracy: ±1 Celsius
Temperature display resolution: 0.1 Celsius
Operating voltage: 2 x 1.5V button LR44 batteries
Dimension: 48×28.6×15.6mm(approx.)
LCD dimension: 36×16mm(approx.)
Operating Voltage: 1.5v, LR44/AG13(Include
Cable length: 1m
Color: Black


Package Content:

1X Mini Thermometer Hygrometer Temperature Meter Digital LCD Display


It does not have a Hygrometer as far as I know.

I opened it up and found this

It has a probe wire length of about 1 meter. I wish to use it to find the temperature in the storage tank of a solar water heater about 20 meters away. My question is - can I just extend the wire (2-core wire) without affecting the temperature measurement? I looked up Amazon product reviews for similar products (not sure they are the same on the inside), but I didn't see any reviewers having extended the wire more than a few feet.

Also, what power supply can I use instead of LR44 cells. I cannot make out the chip inside, though some reviewers on Amazon have stated that anything upto 30 Volts would work.

• Show the wire and the probe please. – Vladimir Cravero Jan 23 '17 at 10:38
• @VladimirCravero - I had to remove the image because I cannot post more than 2 links. Use the first link above that takes you to the Aliexpress product listing which has the pic of the thermometer I'm talking about link – xs400 Jan 23 '17 at 11:02
• It looks like a PTC. Do you have a multimeter? Can you measure the resistance of the probe? – Vladimir Cravero Jan 23 '17 at 11:06
• That sensor could also be a DS18B20 digitial 1-Wire sensor, in which case the data is transmitted digitally over the power line as a series of pulses (shorts). I've got a few with 5 meter cords and fairly thin wires (think CAT5 network cable thickness) and that works fine. 20 meters may push the limit though, as resistance and capacitance of the parallel conductors of the extension cord could distort the signal too much. – JvO Jan 23 '17 at 14:49
• xs400 I bet it was actually 9.9K. And dropping when you put it in your hand means NTC unless your hand is colder than room temperature. – Spehro Pefhany May 7 '17 at 12:33