akaz
New Member
Posts: 3
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Post by akaz on Oct 11, 2022 15:12:46 GMT -5
I am using a Lakeshore 372 Controller and have a ROX thermometer connected to it with a corresponding calibration curve programmed. There is the optional curvature value for doing cubic spline interpolation between the breakpoints, but based on the manual, it should default to a linear interpolation if no curvature value is given (as in my case). As I am changing temperature and monitoring the temperature with my thermometer as a function of time. I am seeing discrete steps at the breakpoint temperatures meaning there is no interpolation happening. Does someone have a possible solution to this. It seems like a setting somewhere in the controller setting the interpolation to 'off', but I can't seem to find anything like that.
Cheers,
Austin
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Post by Lake Shore Jeff M on Oct 12, 2022 6:43:31 GMT -5
Hello Austin, the Interpolation Method is automatically selected based on the curve assigned to the Input so I have a couple of questions:
1. Is the Rox sensor from Lake Shore or from another supplier?
a) if it is from Lake Shore, what is the serial number of the sensor.
2. If it is not from Lake Shore, how do you have the curve file formatted?
a) Standard Rox (non-Curvature) sensor curves require the sensor curve point units (format) be the Base 10 Log Ohm of the
Resistance versus Temperature in Kelvin.
i) This is the format selection log ohm/K where the cubic spline format uses the Ohms/K format (see section 5.6.1 in the
372-user manual).
ii) You cannot enter Cubic Spline curves via the front panel.
Let me know the curve details and we can proceed further. If you have a non-Lake shore curve, please send it to me at support@lakeshore.com
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akaz
New Member
Posts: 3
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Post by akaz on Oct 12, 2022 8:03:55 GMT -5
Thanks for the reply. The ROX is from Lakeshore, serial number RX-102B-CB (U05348). I should also mention that I am seeing this same behavior on two different thermometers (both from Lakeshore), the other one I don't have the serial number on hand, but I think it is either RX-102A or RX-202A (50mK on the low end). If I query the curve points via computer, I get ±123.456E±78,+912.345E±67 as a result, so there shouldn't be any curvature values, thus I am expecting just a linear interpolation between breakpoints. But both thermometers are showing plateaus or discrete steps exactly at the breakpoint values when changing temperature. Any further suggestions would be greatly appreciated.
Cheers,
Austin
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akaz
New Member
Posts: 3
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Post by akaz on Oct 14, 2022 11:49:26 GMT -5
I solved my issue. It was nothing to do with interpolation or the calibration curve. I saw the discrete jumps and plateaus in the measured resistance as well. It seems like as the 372 shuffles through channels 1-8, the channel/thermometer takes a new measurement only when that channel is active. So for instance channel 1 would measure 1kOhm at time = 0 and store that value. I would repeatedly query channel 1 every 5 seconds, and each query would return 1kOhm. It would then take say 60sec for the channels to shuffle through back to channel 1 when it would measure a much different resistance given the temperature change, say 2kOhm. So I would have 12 data points over the course of minute 1 saying channel 1 was measuring 1kOhm, then 12 data points over the course of minute 2 saying channel 1 was reading 2kOhm. Once I disable all other channels besides channel 1, the T/R vs time curve is what I'd expect.
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Post by Lake Shore Jeff M on Oct 14, 2022 12:19:43 GMT -5
That is correct, when you use a scanner, the channel is read and readings are stored in a data register. When you query the channel temperature or sensor value, the information in the register is what is reported. The register is not updated again until the reading sequence connects that channel to the 372 to be read again. Look at section 4.6.1.6.1 Reading Sequence in the Model 372 User Manual for more details on the sequence.
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Post by harrrykeith on Aug 16, 2023 13:53:38 GMT -5
I'm facing a puzzling situation with my Lakeshore 372 Controller and ROX thermometer setup. I've carefully programmed a calibration curve with breakpoints, and from what I understand, the interpolation between these points should default to linear if no curvature value is provided. As I've been changing temperatures and closely monitoring the readings, I'm noticing that the controller is displaying discrete steps at the exact breakpoint temperatures instead of smooth interpolation. It's as if there's no interpolation happening at all.
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Post by Lake Shore Jeff M on Aug 16, 2023 14:23:36 GMT -5
Just to be sure, what format is the curve you entered into the 372 in? Rox sensors require the curve points to be entered as the Log Ohm Base 10 of the resistance versus temperature in Kelvin. The points need to be entered in descending order in regards to temperature, point 1 is the highest temperature and the last poingt is the lowest.
The Model 372 uses the following formula for straight line interpolation:
T=T0+((S-S0)×(T1-T0))/((S1-S0))
In this formula, S is the actual sensor reading, S0 & S1 are the sensor values directly above and below the reading and T0 & T1 are the associated temperature points.
Please send a copy of your curve to support@lakeshore.com so I can verify it is crrect and see if I can duplicate the issue you are reporting/
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