US 4,291,355 A · Programmable overload circuit

Abstract

Disclosed is an overload protective circuit for an electric motor which is adaped to monitor and track motor temperature as a function of an operating parameter, namely armature current. The motor's armature current is sensed and converted to a multi-bit digital signal which is used to address a programmable read only memory (PROM) which has been pre-programmed with discrete digital values of temperature for a plurality of armature currents for the motor being protected. The digital address signal for the armature motor current is periodically updated at a relatively rapid rate and depending upon the armature current sensed, multi-bit temperature values are outputted from the PROM to a digital latch which operates a relatively slower rate to output another address back to the PROM so as to predict what the temperature will be at the next time increment based on the present current value and the present temperature. When predetermined temperature levels are reached, two bits of the PROM's output are respectively adapted to provide an alarm signal, and then a subsequent trip signal which is adapted to deenergize the motor.

Claims15

Dependent claims

An overload protective circuit for a load drawing current from a power source and being operable to effect a predetermined operation in response to a thermal overload condition of said load comprising:

(a) digital memory means programmed with discrete multi-bit data words representative of the temperature characteristic of said load for plural values of load current and being operable in response to an applied address signal corresponding to the value of the present load current and the present load temperature to provide a digital output signal having a predetermined number of bits representative of a predicted load temperature to be reached by said load in a predetermined elapsed time interval and at least one bit adapted to signal a predetermined temperature level being reached by said load;
(b) means providing and coupling a digital signal proportional to the absolute value of the load current to said memory means as a partial address signal;
(c) means coupled to said memory means and being operable to temporarily store said predetermined number of bits of said output signal for said predetermined elapsed time interval and thereafter feed said predetermined number of bits back to said memory means as a partial address signal corresponding to the present load temperature,
said partial address signals being applied concurrently as a composite address signal to said memory means;
and
(d) means responsive to said at least one bit of said digital output signal and being adapted to effect said predetermined operation when said predetermined temperature level is signalled.

3 more elements

An overload protective circuit for an electric motor coupled to a power source through circuit means which are adapted to operate in response to a control signal applied thereto and being operative to disconnect the motor from the power source in response to a predetermined temperature level being reached by said motor and comprisin combination:

(a) means providing an analog signal proportional to the present value of a motor operating parameter;
(b) means coupled to said analog signal and providing a digital signal from said analog signal;
(c) a digital memory including plural input address lines and plural output lines and having selectively addressed plural memory locations programmed with multi-bit digital data words selected bits of which contain discrete motor operating temperature values and at least one bit of which is adapted to signal a thermal overload condition, said at least one bit being adapted to be coupled to a predetermined output line;
(d) means coupling said digital signal to selected ones of said input address lines of said memory to form a first partial address signal for a specific memory location;
(e) a periodically triggered digital data latch having plural input and output lines, said input lines of said latch being coupled to selected ones of said output lines of said memory and said output lines of said latch being coupled to selected other ones of said input address lines of said memory to thereby form a second partial address signal which together with said first partial address signal forms a complete address signal for a specific memory location, whereupon a specific data word is provided to said output lines of said memory at regular time intervals in response to periodic triggering;
and
(f) means coupled to said predetermined output line of said memory and being responsive to a predetermined value of said at least one bit to generate said control signal to disconnect the motor from the power source.

4 more elements

Dependencies are inferred from the claim text.

Programmable overload circuit

Life of this patent

Programmable overload circuit

Life of this patent

Abstract

Claims15