Electronic motor load sensing device

A protection system adapted to be connected to an electric motor and first and second power supply lines, the lines being connectable to an AC power source which supplies a line voltage and a line current, the system comprising:

• line voltage sensing means adapted to be connected to the lines for sensing the voltage therebetween to produce a voltage signal;
• line current sensing means adapted to be connected to one of the power supply lines for sensing the current flowing therein to produce a current signal;
• pulse width modulating means for pulse width modulating one of the voltage or the current signals to produce a pulse width modulated signal;
• modulating means responsive to the pulse width modulated signal for modulating the other of the voltage or current signals to produce a modulated waveform;
• integrating means for integrating the modulated waveform to produce an energy signal;
• detecting means responsive to the energy signal for detecting the existence of an overload or an underload condition;
• and
• disconnecting means responsive to the detecting means for disconnecting the AC power source from the electric motor in response to an overload condition or an underload condition.

A method for controlling a motor connected to a load, wherein the motor is also connected to a power source through first and second power supply lines, the method comprising the steps of:

• developing first and second electrical signals indicative of first and second parameters of power delivered to the motor;
• pulse width modulating the first electrical signal to produce a pulse width modulated first electrical signal;
• modulating the second electrical signal in response to the pulse width modulated first electrical signal to produce a power waveform;
• and
• producing an output signal from the power waveform wherein the output signal is indicative of the energy delivered by the motor to the load.

A method for controlling a motor connected to a load, wherein the motor is also connected to a power source through first and second power supply lines, the method comprising the steps of:

• developing first and second electrical signals indicative of first and second parameters of power delivered to the motor;
• pulse width modulating the first electrical signal to produce a pulse width modulated first electrical signal;
• modulating the second electrical signal in response to the pulse width modulated first electrical signal to produce a power waveform;
• and
• producing an output signal from the power waveform wherein the output signal is indicative of the energy delivered by the motor to the load;
• and
• further including the steps of providing power for a short duration of time when a switch interrupts power flow through one of the power supply lines, producing a further signal indicative of the number of times within a predetermined amount of time that the switch has consecutively interrupted and re-enabled the flow of power through the power supply lines within the short duration of time and controlling the power delivered to the motor in response to the further signal to prevent rapid cycling of the motor.

A device adapted to be connected to a motor which is coupled to a load for measuring energy delivered by the motor to the load and further adapted to be connected to a switch which alternatively disconnects the device from and reconnects the device to a power source, wherein the motor is adapted to be connected between first and second power supply lines connected to the power source, the device comprising:

• developing means for developing first and second electrical signals indicative of first and second parameters of power delivered to the load;
• pulse width modulating means for pulse width modulating the first electrical signal to produce a pulse width modulated first electrical signal;
• modulating means responsive to the pulse width modulated first electrical signal for modulating the second electrical signal to produce a power waveform;
• producing means responsive to the power waveform for producing an output signal indicative of the energy delivered by the motor to the load;
• controlling means responsive to the output signal for controlling the power delivered to the motor;
• and
• means for preventing rapid cycling of the motor including means for providing power for a short duration of time when the switch disconnects the device from the power source and means for indicating the number of times within a predetermined amount of time that the switch has disconnected the device from and reconnected the device to the power source within the short duration of time;
• wherein the controlling means is further responsive to the indicating means to disconnect the power source from the motor when the power source has been disconnected from and reconnected to the device a present number of times during the predetermined amount of time.

A motor protection device adapted to be connected between a motor and a switch which disconnects a power source from the motor protection device in response to a first condition and which reconnects the power source to the motor protection device in response to a second condition, wherein the motor protection device is adapted to prevent rapid cycling of the motor, the motor protection device comprising;

• means for providing power for a short duration of time when the power source is disconnected from the motor protection device;
• means for storing a signal indicative of the number of times within a predetermined amount of time that the power source is both disconnected from the motor protection device and reconnected to the motor protection device within an amount of time equal to the short duration of time;
• and
• means response to the signal for disconnecting the motor from the power source when the power source has been disconnected from and reconnected to the motor protection device a preset number of times during the predetermined amount of time.

A device for measuring the torque delivered by a motor to a load, comprising:

• first measuring means for measuring a first parameter of power across the motor to develop a first signal;
• second measuring means for measuring a second parameter of power across the motor to develop a second signal;
• a pulse width modulator responsive to the first signal for producing a pulse width modulated signal;
• a modulator responsive to the second signal and to the pulse width modulated signal for modulating the second signal;
• and
• a phase shifter connected between either the first measuring means and the pulse width modulator or the second measuring means and the modulator for phase shifting one of the first or second signals.