FAQ
Calibration
What is a Measuring Chain?
The temperature data used to monitor or control your process results from a sensor transmitting a signal to an electronic device (panel meter, chart recorder, or PLC). All components involved with the measurement are responsible for the accuracy of the data. From the tip of each sensor, via the connecting wires, signal interface, analog to digital conversion, conversion from millivolts to temperature, to display and printout of the measured values are referred to as the Measuring Chain.
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What equipment do I need to calibrate a Measuring Chain?
The measurements generated by your measuring chain need to be compared with an independent measurement that is traceable to a recognized standard. Therefore, you need a Secondary Temperature Standard connected to a device that can display temperature.
Place the Standard and the sensor being calibrated into a reference unit, let them stabilize, and compare readings. As a result, you can adjust your meter or control device to read the same temperature as the Standard. You now have calibrated your measuring chain at one temperature point. This point is typically near the temperature of use in the process. If process temperature varies over a wide range, then you need to perform this procedure at a low and a high temperature.
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How can I check the accuracy of my IRTD?
An IRTD used outside the laboratory is referred to as a traveling standard, while an IRTD that remains in one location is called a stationary standard. The traveling standard can easily be checked against the stationary standard using the IRTDWin™ software, which will allow you to generate an automatic comparison and document the results.
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Is the CTR-80 Temperature Bath compatible with older Validator systems?
The CTR-80 is fully compatible with earlier Validator systems using Windows software version 1.09 or later. Systems using DOS software operate in semi-automatic mode during sensor calibration. Simply set the bath manually to the value you entered for the calibration point in Setup. The software will complete the calibration for that point. Repeat the process for your second calibration point.
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How is an IRTD Temperature Standard calibrated?
Kaye maintains two temperature calibration laboratories: NIST-traceable at the company headquarters in N.Billerica, MA, and DKD-certified at Kaye Instruments GmbH, Pforzheim, Germany. Each calibration results in a certificate with traceability to NIST or PTB standards, respectively.
When an IRTD Temperature Standard is received at Kaye Instruments for service, repair or calibration, our certified temperature calibration laboratory performs the following steps:
- Generates a printout of all IRTD parameters as received such as its address, baud rate and label. This provides a record for assisting in any troubleshooting if required.
- Inspects the stainless steel stem for damage (nicks, kinks, or bends) and verifies the integrity of the stem seal. If the customer requests, the EPROM memory (firmware) is updated to the latest revision for that particular IRTD design. Contact customer service for the price to upgrade firmware.
- The IRTD is annealed to remove any stresses created by thermal or mechanical shock. Typically, this process involves heating in a salt bath at 395 to 400°C for a minimum of 30 hours. Data, collected every minute, is graphed until a smooth curve is observed, indicating proper annealing has occurred. The plot indicates rate of change of resistance in the sensing element, which determines whether annealing was successful. In extreme cases where a smooth curve is not obtained, an extended anneal cycle of up to 100 hours is performed. If the customer requests, Kaye provides "as found" data recorded before the annealing process.
- After the IRTD passes the annealing process, it is calibrated at 4 points. The IRTD is allowed to stabilize (about 30 minutes) at the following reference points: -195°C (liquid Nitrogen), 0°C (ice bath), 100°C (oil bath), and 400°C (salt bath). This is followed by a Post-Calibration conformance check.
- The last step is to generate a NIST-traceable Calibration Certificate.
With Kaye's inspection, annealing, calibration, and verification process, you receive an IRTD that not only meets specifications, but also maintains its accuracy during the recommended 1-year calibration period. Other calibration labs will typically not perform an annealing process as described in #3 above. Because their procedures only check the IRTD at specific points, any build-up of stress from previous use still remains. This increases the potential for the IRTD to go out of calibration sooner when it is subjected to additional stress.
At Kaye, the annealing process relieves the stress resulting from mechanical and thermal shock before the IRTD is calibrated. Essentially, annealing resets the stress level to zero, ensuring that the calibrated IRTD remains within tolerance.
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How long does a Kaye Teflon probe need to stabilize, going from room temperature into a HTR/LTR at 121°C?
If your temperature reference is already stable at 121°C, the thermocouple should stabilize within three to five minutes after inserting thermocouples at ambient. A probe with a leak in the insulation (moisture in the tip), will not stabilize in this time frame. If you use Kaye's software for automated sensor calibration, it automatically monitors probe stability and captures the data until stability is achieved.
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