Best way to get started with an RTD and Temp Monitor 218

Hi Jeff,

Nice idea starting out with a bench test. Using the platinum sensor will give you experience wiring up your connector in a 4-lead configuration like Jeff M suggested (see section 3.3.2.5 of the manual) and will give you experience configuring the 218 for that sensor. I'd suggest connecting the sensor to the Input 1 pins (pins 3, 4, 15, 16) of the 25-pin connector (see section 3.3.2.1 of the manual).

Once physically connected, it's going to be easy to set up since the platinum sensor follows a standard curve and you only need to set the Sensor Input Type to 250 Ohm Plat (see section 4.5 of the manual). As soon as you do this for Input 1, your 218 should now be reporting the resistance of the sensor, which would be around 110 Ω at room temperature.

The next step will be to tell the instrument that this is a PT-100 series sensor so that it can report in temperature units (kelvins by default). Section 4.6 of the manual will show you how to do this, you'll want to select Curve Number 6 so that PT-100 is displayed on the screen. Once you've assigned this curve to input 1, your home screen should now be showing a room temperature reading in Kelvin. Now you're ready for the big league.

Cernox sensor are a little more complicated unfortunately, they don't use a standard curve so you'll need to load the sensor's calibration curve onto the instrument. Before you do this though, you should change the Input type (section 4.5) to Cernox. So the 218 supplies the sensor with the correct excitation.

Now you'll need to use our Curve Handler software (free) to load your calibration curve onto the instrument. Hopefully you have something on hand to communicate with an RS-232 DB9 serial port. The 218 is one of our older instruments, so it's not very user friendly to get this done. To quote the manual:

The curve format you'll want to use is the .340 file that should have come with your calibrated Cernox sensor. Let me know if you have an issue with any of this. It definitely confused me the first time I tried to use a 218.

Use the process in section 4.6 again to select this new user curve for input 1, then you should be back to seeing a real sensor temperature on your front screen. At this point, I'd suggest reading chapter 2 of the manual for a primer on working with cryogenic environments if you don't have that background already.

Just a quick warning too: Take a look at your Cernox calibration document and make sure that the Cernox sensor doesn't exceed 7500 Ω at the temperatures you're expecting to measure. If you're measuring a low temperature superconductor, you might be seeing temperatures that would cause some Cernox sensors to overload the Model 218 monitor. If this is the case, I'd suggest getting a calibrated DT-670 silicon diode sensor instead. They can measure down to 1.4 K on the 218 and will generally cost less than a Cernox. They just aren't any good in magnetic fields.

Hopefully this is helpful in getting you going with the 218. It's hard to give a thorough run down of our instruments in a single forum post. Please let me know how you go, I'm writing this all without a 218 running next to me, so hopefully I'm not leading you astray with my suggestions .