Lyophilization of Pharmaceuticals II

A description is presented of the circuitry, design, and operating characteristics of a temperature-conductivity bridge especially fabricated for eutectic and freezing-point temperature measurements. The resistance bridge is capable of measuring accurately from 10 3 to 10 12 ohms over a temperature range from −50° to +50°. A d.c. applied potential of 1, 10, or 100 v. is used as a power supply, and a solidstate operational amplifier is employed as the detecting system. By employing a high-gain amplifier with an input impedance in excess of 10 8 ohms, stable power supplies, and special insulation design, it is possible to cover the range from 10 3 to 10 12 ohms in narrow- or wide-range decade steps. The circuitry of the temperature-conductivity plotter permits temperature measurement by either thermocouple or thermistor circuits. The information obtained is displayed on a X - Y recorder with variable sensitivity.