. Biophysical research methods. Biophysics -- Research. 158 LAWRENCE R. PROUTY AND JAMES D. HARDY equals arm 4. This condition is obtained when the variable resist- ance oi AB equals the varying resistance of the detector coil, BT. Direct temperature readings at T (rather than ohms) are possible with proper calibration of the slide wire, which constitutes the vari- able section of the resistance of arm 3. Although the above circuit is the most generally satisfactory for ordinary biophysical work, precision resistance thermometry em- ploying a platinum \vire thermometer requires somewhat differ
. Biophysical research methods. Biophysics -- Research. 158 LAWRENCE R. PROUTY AND JAMES D. HARDY equals arm 4. This condition is obtained when the variable resist- ance oi AB equals the varying resistance of the detector coil, BT. Direct temperature readings at T (rather than ohms) are possible with proper calibration of the slide wire, which constitutes the vari- able section of the resistance of arm 3. Although the above circuit is the most generally satisfactory for ordinary biophysical work, precision resistance thermometry em- ploying a platinum \vire thermometer requires somewhat different circuits. The basic operation of precision resistance thermometry consists in the measurement of the potential drop across the resistance thermometer as compared to that across a standard resistor. Either a potentiometer or a bridge circuit can be used. The potentiometer. Arm 3 Arm A Fig. 11. Commonly used Wheat- stone bridge circuit for three lead re- sistance thermometer (modeled after a Leeds and Northrup circuit). is a more versatile instrument capable of measuring temperatures over a greater range than a bridge circuit with equal sensitivity, but is somewhat more difficult to use. In the potentiometric method the voltage drop across two resistors carrying the same current is measured. One of these resistors is a standard of the four terminal type and the other is the resistance thermometer. Both are con- nected in series with a battery. Resistance thermometers for use in the biophysical temperature range usually have a potential drop of V. or less and are best used with low voltage potentiometers. Mueller (^4) states that for accuracy of °C. in temperature de- termination, resistance measurements must be made with an accu- racy of two to four parts in a Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemb
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