Calibration thermocouple

Thrner gauges may be used to determine scale thickness in situ. These are Wheatstone bridge circuit devices that have proved very useful for 40 years or so. As with chloral thermocouples, calibration may be difficult, and the level of magnetic iron content (magnetite) in the deposit may affect the readings. More modem electronic versions, similar to paint thickness testers, are now available. 

Thermocouples calibration check report after test... 

Thermocouple calibration report before test (SIP and temperature distribution study)... 

Printout for thermocouple calibration checks after study... 

Accuracy of thermocouples should be 0.5°C. Temperature accuracy is especially important in steam sterilization validation because an error of just 0.1 °C in temperature measured by a faulty thermocouple will produce a 2.3% error in the calculated F0 value. Thermocouple accuracy is determined using National Bureau of Standards (NBS) traceable constant temperature calibration instruments such as those shown in Figure 6. Thermocouples should be calibrated before and after a validation experiment at two temperatures 0°C and 125°C. The newer temperature-recording devices are capable of automatically correcting temperature or slight errors in the thermocouple calibration. Any thermocouple that senses a temperature of more than 0.5°C away from the calibration temperature bath should be discarded. Stricter limits (i.e., <0.5°C) may be imposed according to the user s experience and expectations. Temperature recorders should be capable of printing temperature data in 0.1 °C increments. 

The present work involves measurement of k in a 0.1 atmosphere, stoichiometric CH -Air flame. All experiments were conducted using 3 inch diameter water-cooled sintered copper burners. Data obtained in our study include (a) temperature profiles obtained by coated miniature thermocouples calibrated by sodium line reversal, (b) NO and composition profiles obtained using molecular beam sampling mass spectrometry and microprobe sampling with chemiluminescent analysis and (c) OH profiles obtained by absorption spectroscopy using an OH resonance lamp. Several flame studies (4) have demonstrated the applicability of partial equilibrium in the post reaction zone of low pressure flames and therefore the (OH) profile can be used to obtain the (0) profile with high accuracy. 

At a basic level, it seems that one should be able to take any thermocouple, attach it to a voltmeter, and determine the amount of electricity generated from the heat applied to the dissimilar junction. Then the user could look in some predetermined thermocouple calibration table to determine the amount of heat that the amount of electricity from that specific type of joined wires produces. 

Thermocouple calibration tables have been compiled by the NIST and can be found in a variety of sources such as the Handbook of Chemistry and Physics by the Chemical Rubber Company, published yearly. 

If you look at a thermocouple calibration table, you will see that it has a reference junction at 0°C. This reference point is used because of an interesting complication that arises when a thermocouple is hooked up to a voltmeter. To explain this phenomenon, first look at one specific type of thermocouple, a type T (cop-per-constantan design). Also, assume that the wires in the voltmeter are all copper. Once the thermocouple is hooked to the voltmeter, we end up having a total of three junctions (see Fig. 2.31) ... 

The main source of uncertainty was the absolute temperature measurement, which was made with a platinum, platinum-rhodium thermocouple, calibrated by the National Bureau of Standards to i but thought to be accurate to 1 ° G. AZ/q was obtained l y substituting the experimentally determined equilibrium constants and the spectroscopically derived free energy functions into equation 3.1.6. The results obtained are shown in Table 3.2.1. 

The heat transfer coefficients h are shown in Figures 3, 4, 5 and 6 plotted against AT - T - Tg. For small AT, accuracy is limited by thermocouple calibration error, which we estimate to be within 0.2 K. Thus, estimated errors in h range from 2 % at AT - 30 K, to ... 

Temperature was measured using a Pt-PtlORh thermocouple, calibrated to the melting point of silver. The hot junction was placed about 3 mm below the bottom of the cell. Temperature was kept constant within 0.5 K by means of an electronic controller connected to a separate thermocouple. 

The temperature was measured by a Pt-PtlORh thermocouple, calibrated against the melting point of silver. The thermo-voltage was indicated by a digital voltmeter. The temperature variation over the length of the boat was less than 1°C. During the measurements, the temperature was kept constant within 0.5°C by the use of Eurotherm PID-controller, Model 070. 

Portable thermocouple calibrator set to 150°F with a thermocouple inserted into it. 

As with any instrument, calibration is important for thermocouples. Although manufacturers supply accuracy data for typical thermocouples, calibration can be used to check that these data apply to the specific instrument being used in an experiment. The accuracy can be improved by calibrating the specific thermocouple being used. More importantly, a thermocouple calibrator (see Figure 5.5) can be used to check for any wiring problems or any setup mistakes in the data acquisition system. A thermocouple that has been wired and connected to the data acquisition system can be inserted into the calibrator to check for problems. For example, if a Type R thermocouple is actually being used but it... 

---