Abstract: A thermocouple circuit has dissimilar conductors joined to form a conventional temperature transducer located in a zone to be monitored or controlled. The opposite ends of these conductors are connected to similar metal leads in a capsule located in a stable oven to form a reference junction. The oven also houses an inexpensive integrated circuit operational amplifier which is electrically connected to the similar metal leads to yield a high gain output signal proportional to the weak thermal e.m.f. in the dissimilar conductors. This signal is compared to a preset reference voltage level and the difference signal converted to a temperature correction signal which is in binary form. The oven, the operational amplifier, and the binary signal producing circuitry are all driven by a power source which has as its reference or common potential an isolated voltage level tapped off the shielded secondary winding of an otherwise conventional transformer.

Abstract: Circuitry is disclosed that monitors the frequency at which a heater controller applies pulses to a heater to determine if the heater controller is operating properly. If the heater controller fails to generate a pulse in a selected interval, the circuitry generates a signal that activates an alarm and interrupts the operation of a machine that is processing material heated by the heater.

Abstract: An electric toaster in which a toast support bar is held down by an energized electric magnet so as to maintain bread, on the support bar, alongside electric heating elements. When the bread has been toasted to the desired degree, the electromagnet is de-energized, permitting springs to lift the support bar to pop-up the toast. The rising movement of the support bar causes a switch to operate which interrupts the electrical supply to the elements.