print118 - 8-7-2024 at 12:18
Hello,
I have a IKA C-MAG HS 7 digital hotplate stirrer and I'm planning on getting it a temperature sensor, only problem is that the ones from IKA cost a
lot and I can't find them cheaper even on Ebay, so I intend to build my own. The sensor is a PT1000.
I've seen NurdRage's video on how to build your own temperature probe, but compared to his hotplate, when testing the probe connection port on the
hotplate with a known resistor to see which contacts do what I discovered that there are multiple ways I can connect the the resistor to get the
hotplate to think I connected a real probe. All of the connections gave slightly different temperature readings (some 0.5K apart).
So my question is, does anyone know precisely how the IKA PT1000 temperature probes are built and wired? Are they 2-wire, 3 wire or 4-wire? And how
the connections are wired. If anybody happens to have the specific probe, I would be very happy if you could do some testing on the wiring of said
probe.
Thanks in advance for your responses.
Rainwater - 8-7-2024 at 12:50
They can be 2,3 or 4 wire. All depends on precision.
A two wire (-/+)reads the voltage drop across the entire appratus. Connector, lead, sensor. And is the least accurate
A three wire (-/V/+) takes 2 measurements, the first is the total voltage drop, just like the two wire, then a voltage measurement at the point of
contact at the sensor. This voltage drop is multiplied by 2 then subtracted from the total drop.
The idea is, both leads will be equal impedance, so if you find one, and assume the other, you can remove this error from your reading.
A 4 wire(-A/+A/-V/+V) pumps current through one set of wires (-A/+A) and directly measures the voltage drop across the resistor (-V/+V).
A higher impedance volt meter can be used for a 4w vs a 3w configuration and a clever engineering can arrange the plug so that all configurations can
be used with one plug. For a $1400 stirrer, id expect that to be the case.
Crack that baby open and send some pictures.
Remimber, warranty stickers are optional
[Edited on 8-7-2024 by Rainwater]