A computer controlled, laboratory heat-sealing machine is employed as a quality control device to ensure that adequate heat seals are formed under pre-defined and outputted pressure, dwell time and temperature parameters. The apparatus includes sensors for monitoring temperature and pressure conditions throughout the sealing dwell period. The clamping pressure is constantly adjusted to be maintained at a preset level by sensing the clamping pressure and controlling the top heat-sealing bar through an eccentrically driven crankshaft linkage. Load cell arrangements for monitoring pressure in high and low pressure ranges are also disclosed.