A detailed description of the digital control for a differential scann
ing microcalorimeter to be used in the study of biomolecules is given.
Three control loops and an adequate control program ensure that the i
nstrument works under adiabatic conditions and the temperature differe
nce between the sample and reference cells is as close as possible to
zero. A static and dynamic characterization of the instrument is also
described. The gain of the control loop can be selected by the operato
r, thus changing the calibration constant, signal/noise ratio (SNR) an
d time constant of the instrument according to experimental requiremen
ts. Some characteristics of the instrument are: (a) any scan rate betw
een 0.1 and 2 K min(-1), with deviations from linearity and reproducib
ility about 0.2-0.3%, can be selected; (b) its calibration constants a
t each scan rate are highly reproducible (about 0.4%); (c) the reprodu
cibility of the instrument upon refilling of the cells is about 10 mu
J K-1; (d) the noise in the sensor is about 2 nV; and (e) the time con
stant of the instrument changes from 7 to 70 s depending on the contro
l loop gain used.