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Classic FieldPoint FP-TC-120 Product Notification Information

Hardware: FieldPoint>>Analog I/O Modules>>FP-TC-120

Problem:
As expressed in our recent product notification letter, we recently discovered that revisions A and B of classic FP-TC-120 modules have a predictable offset that is a function of the operating temperature when operating in environments below 13.4 °C and above 30.5 °C. This issue does not require repair and can be resolved by downloading a VI that compensates for the error.

Solution:
To find out if your classic FP-TC-120 behaves incorrectly, look at the part number printed on the module. The revision is the letter in the part number. The revision A and revision B FP-TC-120 modules have part numbers 184522A-01 and 184522B-01 respectively. This issue does not exist on the current shipping revision.

The cold-junction (CJ) reading of revisions A and B of the FP-TC-120 has an additional error of up to 1.8 °C or –3.5 °C at the ends of the operating temperature range, as the chart below shows.

The additional CJ error does not have a one-to-one correlation with errors you see in measurements. Below are charts for many common thermocouple types and the additional CJ errors at specific measurement temperatures. These charts are based on the assumption that the ambient temperature of your FieldPoint system is 30.5 °C or 13.4 °C, which results in 0.5 °C of additional error. For example, if your system is operating at a temperature of 40 °C, your measurements have –1 °C of additional CJ error (from the chart above). If you are using a J-type thermocouple and taking measurements at about 800 °C, the measurements have an additional error of 0.8 °C:

1 °C/0.5 °C = 2; 2 × 0.4 °C = 0.8 °C.

Note: Use the Word document entitled TC-120 Graphs attached to this article for a better view of these graphs.

Not all applications are affected by this issue. The following applications will operate properly with the additional error uncorrected:

• Applications in which the ambient temperature of the FieldPoint system is near room temperature and the specific additional error for your thermocouple type and measurement range is acceptable
• Applications that measure relative temperatures or changes in temperature rather than absolute temperature

If you believe this problem affects your application, you can correct the offset in software. Attached is a zip file containing a VI that can be used in existing applications to correct the offset in revisions A and B of the FP-TC-120. The zip file also contains an example VI that demonstrates how to use the offset correction VI in an application.

Using the TC-120 Rev A & B Offset Adjustment VI in the attached zip file you should expect to see the correction in the chart below. The blue line is the total uncorrected temperature error that you may see without the TC-120 Rev A & B Offset Adjustment VI. The pink line indicates the total temperature error that you may see with the adjustment VI.

Please accept our apology for the inconvenience. National Instruments is committed to your total satisfaction and to maintaining your confidence in our products. We have re-validated this product’s specifications and corrected its test plan. If you have any questions or concerns, please contact the FieldPoint Product Support Engineer.

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Report Date: 05/27/2005
Last Updated: 05/30/2006
Document ID: 3LQEUUVM

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