Pulsed-Current Control and Measurement System for Precision Microcalorimetry

Publisher Website
Google Scholar
Abstract
Instrumentation for heat measurement in differential microcalorimetry is described in sufficient detail so the electronic apparatus can be built and used reliably with various calorimeters. Theory and calibration techniques are explained for calculating endothermic and exothermic heats from indicated digital data for reactioncalorimetry and temperature scan calorimetry (including DTA). The cooler of twin calorimeter cells is heated electrically to counteract thermal effects of the system being measured. This heating is by pulses of current, all identical, whose rate of occurrence is controlled proportionally to the small residual intercell temperature gradient; counting pulses gives heat indication directly as numbers. The heat per pulse is known accurately, and the pulsed (indicated) heat is related to effects of the system under study; the relation is by a constant, near unity factor (such as 1.010) which can be calculated using easily measuredcalorimeter parameters. The factor is constant because heating is proportional to the residual temperature gradient, and differs from unity because of heat conduction through that gradient. Over‐all accuracy, experimentally confirmed, exceeds 0.1% and depends on well‐standardized electrical measurements, so calorimetric calibrations are not needed with calorimeters of known material capacity. Pulses, 16.666 msec long, occur at rates up to 30/sec and have switch‐selected amplitudes from 0.02 to 640 μcal per pulse (60 Ω heater). Equipment design includes devices for routine tests to detect component deterioration before it has become serious.

This publication has 8 references indexed in Scilit: