Thermocouple calibration, errors

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 ... 

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. 

Errors in the Electronic Thermocouple Calibration The thermocouple interfaces with the computer via an analog-to-digital conversion board. Since the thermocouple s output is in millivolts, the interface board will linearize and set the limits of the signal. The instrument usually also will... 

G. Temperature Determinations. In vacuum line work it is frequently necessary to measure low temperatures. While the mercury-in-glass thermometer is convenient, it does not extend below the freezing point of mercury, — 38.9°. Pentane-in-glass thermometers have a similar convenience and may be used down to about — 150°C, but they are only useful for rough work (an error of 5°C is common). For more precise determinations, a calibrated thermocouple or thermistor, or a vapor pressure thermometer, is useful. 

The sample temperature,measured with calibrated thermocouples directly inserted into the specimen, was known with an error of +0.05 °C throughout the whole temperature interval investigated. 

The decomposition temperatures of hydrates were measured by means of differential thermal analysis (DTA) under the conditions of excess gas in a stainless steel flask that was developed specially for the investigation of hydrate formation with a gaseous guest at high hydrostatic pressure. The hydrate decomposition temperature was measured with a chromel-alumel thermocouple to the accuracy of 0.3 K. The thermocouple was calibrated with the use of temperature standards. Pressure was measured with a Bourdon-tube pressure gauge. The error of the pressure measurements did not exceed 0.5 %. This procedure was described in more detail previously.The gases used in the investigation... 

Figure 13 shows temperature profiles that were obtained for well GTW-2 using the optrode and the thermocouple. The optrode temperature value is plotted as open diamonds. The thermocouple readout is plotted as c ien squares. Measurements were made to a depth of 150 m (about 490 ft). The agreement between the optical measurements and the thermocouple measurements is within the error of the calibration data ( 2 C). 

Fixed error in the system could arise from two sources First, the dewar volume in the cylindrical test section was known with an accuracy of only 0.1 by water calibration at room temperature second, the thermocouple spacing measurement was accurate to only )i6-in. Percentage error in the volumetric measurements was, therefore, afunctionof the total change of liquid level for any given test and varied from 0.4 at the high flow rates to 1.4 at the lower values. 

Consistency, however, only runs to one compound and is not present from one compound to the next. To explain this further, a thermocouple error of x °C on one compound will always be x 1.5 °C for that compound and thermocouple. For another compound the error on the same thermocouple will not be x °C, but will consistently be y 1.3 °C. Hence for control purposes an indicated mixing temperature can be relied upon, providing the discrepancy from true batch temperature has been calibrated for all compounds, and again on installation of a new thermocouple probe. 

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