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Post by suplab on Oct 1, 2019 4:37:25 GMT -5
Hello Can anyone help me with the insertion of calibration curve for cernox RTD in Lakeshore 350 Temperature controller. I have the excel file for temperature(in K) against resistance(in ohms) for the cernox 1050-aa which was uncalibrated initially and also the controller does not have the calibration records for this particular sensor. I need to know how to feed the data in my excel sheet to the temperature controller in one of the curve slots. Hope someone helps me with this. Thanks  |
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Post by Lake Shore Jeff M on Oct 1, 2019 6:35:13 GMT -5
For a Cernox sensor, the Model 350 requires that the curve data points be in the format of Log Ohms (Base 10 of the resistance) versus Temperature in Kelvin. The easiest way to enter the curve is to use the Lake Shore Curve Handler Application which you can install from www.lakeshore.com/resources/software/curve-handler. Once you have the application installed and connected to the Model 350, you can then use any text editor to create a text file with the following format: Sensor Model: CX-XXXX-XX-XXX Serial Number: XXXXXX Data Format: 4 (Log Ohms/Kelvin) SetPoint Limit: 330.0 (Kelvin) Temperature coefficient: 1 (Negative) Number of Breakpoints: XX No. Units Temperature (K) 1 1.73936 330.715 2 1.74412 326.059 3 1.75062 319.910 4 1.75594 314.899 5 1.76139 309.916 6 1.77285 299.882 The top portion is the header so you would replace the X's with appropriate information for your sensor. As you can see, the breakpoints are entered from the highest temperature down to the lowest. The sensor units are the base 10 log ohm value for the resistance. Once you have all of the breakpoints entered, make sure you enter the number of points in the header. Next change the file name from .txt to .340 and then read the file into the Curve Handler application. Verify that the graph of the curve looks smooth and then load it into the Model 350. You can also use the curve handler application to build the curve by entering points one at a time again starting with the highest temperature down to the lowest. For additional assistance, please send an email to support@lakeshore.com and we will assist as requested. |
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Post by suplab on Oct 16, 2019 23:25:11 GMT -5
Is it required to arrange the temperature values in descending/ascending order or the order does not matter as long as the the corresponding resistance values are correct?
Is there a limit on the maximum/minimum number of data points or one can provide as many data points for better calibration?
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Post by Lake Shore Jeff M on Oct 17, 2019 5:52:14 GMT -5
Yes, the order that the temperature values are to be entered will depend on what type of sensor you are using. For Negative Temperature Coefficient (NTC) sensors like a Cernox sensor, the temperature values must be entered in descending order (highest to lowest temperature) and the sensor units must be the Log Ohm Base 10 value of the resistance. For Positive Temperature Coefficient (PTC) sensors like our PT-100 Platinum sensors, the points need to be entered in ascending value (lowest to highest) and the sensor value the actual sensor resistance.
The Model 350 can hold up to 39 user entered curves and each of the user curve can contain a maximum of 200 points.
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pazhk
New Member
Posts: 1
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Post by pazhk on Jan 14, 2021 10:56:39 GMT -5
Hi,
I have a related question. We've recently upgraded from Model 340 to Model 224. The old model has a custom curve for a NTC RTD sensor, but it is a "positive" curve and the units are Ohm/K.
As a test, I've selected PTC RTD on 224 and the curve was accepted and the temperatures read are reasonable.
Do I need to convert the curve to log(Ohm)/K and reverse the order to make it "negative"?
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Post by Lake Shore Jeff M on Jan 21, 2021 8:30:53 GMT -5
No PTC RTD sensors use the Ohms versus temperature in Kelvin format. The LogOhms/Temperature format is only used for NTC RTD sensors
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