Thermometers, recording type

There are two types of devices subject to calibration those that are adjustable and those that are not. An adjustable device is one where the scale or the mechanism is capable of adjustment (e.g. micrometer, voltmeter, load cell). For non-adjustable devices a record of the errors observed against a known standard can be produced which can be taken into account when using the device (e.g. slip gage, plug gage, surface table, thermometer). 

In the field, all types of freezer storage facilities are used. The investigator may have a food freezer at his home that Is used for residue samples or the freezer may be in a rented mini-storage warehouse across the city from his home. The samples may be stored in a commercial freezer facility, In a walk-in freezer at a university, or some other facility chosen by the field investigator. Each freezer is equipped with a recording thermometer. Each time the chart is changed, the calibration is checked with a mercury thermometer and the reading recorded. All freezer records are retained in the data archive. 

Most laboratory thermometers have a mark around the stem that is three inches (76 mm) from the bottom of the bulb. This is the immersion line the thermometer will record accurate temperatures if immersed to this line. If the thermometer happens to be of the total immersion type then the readings will need to be corrected when taking melting and boiling points... 

On account of the mechanical construction of pressure thermometers, both as regards the mechanism for indicating and recording and the necessity for using comparatively large and heavy bulbs, the accuracy that can be secured with this type... 

The second type of test we run on the Sikarex is an adiabatic test. In this test the jacket temperature is controlled by the sample temperature. When the sample thermometer detects an increase in the sample s temperature, the jacket temperature is increased an equal amount. In other words, the sample is being held under adiabatic conditions. The test is run by step-heating the sample into the exotherm detection range found in the previous Sikarex test by means of a heating coil attached to the sample tube. External heating is then stopped, and the sample is allowed to self-heat. The adiabatic temperature rise of both the jacket and sample are recorded. 

Thermocouples tend to be relatively inexpensive, bnt the instruments to measure voltages and to record the temperatnres are generally more expensive. To obtain reliable temperature measurements, the following factors are important relative to the installation of the thermocouple plus other types of thermometers ... 

Quite often the measurement of temperature during the course of an experiment is a continuous process, and, in addition, it is not an isolated event but is to be related to other events. Consequently, it is desirable to have a method of recording the temperature readings over a period of time without operator attention. Many of the thermometers available accommodate this by providing some type of output that is directly related to temperature. 

A bimetallic thermometer (Fig. M-7) consists of an indicating or recording device, a sensing element called a bimetallic-thermometer bulb, and a means for operatively connecting the two. Operation depends upon the difference in thermal expansion of two metals. The most common type of bimetallic thermometer used in industrial applications is one in which a strip of composite material is wound in the form of a helix or helices. The composite material consists of dissimilar metals that... 

The stability over the course of the process was evaluated by Mitrus [1] on the basis of temperature changes recorded in each extruder section in the processing of all the applied materials with difierent process parameters. The stability of temperature behavior of a final product immediately after it had left the extruder die was also studied. Temperatures in the cylinder were measured by means of thermocouples fixed in each section and connected to meters installed in the extruder control board. The product temperature was recorded with a digital thermometer (CIE 370 type) equipped with an appropriate measuring lance. All the data were registered by PC. 

FIGURE 18.4 Differential scanning calorimeter (power compensation type). The platinum resistance thermometer (PRT) sensor detects a small error signal between the programmed temperature and the sample temperature and calls for more or less power to each heater to keep both holders on program. The difference in power required between the sample and the reference is amplified and recorded. (Courtesy of PerkinElmer Corporation, Norwalk, CT.)... 

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