Abstract: A heater-scale having a curved supporting member upon which a bag of fluid to be heated can be placed, has a distributed two-dimensional heating element affixed to a lower surface thereof. The curved member is supported by a load cell for generating an electrical signal proportional to the weight of the bag on the heater member, a thermistor is in contact with the fluid whose temperature is to be maintained, a thermistor is affixed to the heater member, and a control system senses the weight and temperature of the bag of fluid as well as the temperature of the heater member for the purpose of nonlinearly adjusting the electrical current supplied to the heater element as fluid is removed from or variable temperature fluid is added to the bag so as to maintain the bag at a predetermined temperature.

Abstract: A self-checking timer usable with a host system includes a clock and a plurality of interconnected counters. During a power-up phase the timer generates a system reset signal and counts the counters in a predetermined sequence. A flip-flop is set and reset during the power-up phase and inhibits generation of the system reset signal. During a normal operating phase, the timer generates a test signal that must be responded to by the host system to continuously inhibit generation of the system reset signal.

Abstract: A switch and decoder circuit and method of reading same includes a 4 to 16 line decoder latch for selectively enabling up to 14 manually settable switches, each of which generates a BCD code in response to a switch setting, a plurality of thumb wheel switches each of which is selectively enabled by the decoder latch are connected in parallel to a data bus which can then be sensed by associated circuitry. Two pseudoswitches are provided which may be selectively enabled by the decoder latch and which gate onto the address bus two known, non-BCD codes for hardware checking purposes. A control program in an associated processing unit through input/output circuitry can select a switch whose outputs are to be sensed, read asserted and negated values for the switch, compare the values to a predetermined range of allowable values, and cycle the pseudoswitches to determine whether or not the hardware is functioning properly.

Abstract: A hand-held digital readout thermometer measures temperatures over the range -50.degree. C. to +1100.degree. C. with a maximum error less than 3.degree. C. in that range. The thermometer includes a thermocouple, a temperature stable and temperature independent power supply, a temperature stable differential first amplifier, a second amplifier that compensates for the nonlinear response of thermocouple voltage to temperature, and an analog/digital converter controlling a digital display indicating temperature according to a preselected scale. A particular feature of the invention is a latching comparator capable of activating a low battery indicator when the supply voltage drops below a preselected value.