Electronic circuits for temperature control

Claim 3

A method according to claim 1, of maintaining a body of hot glass at a desired viscosity, including the steps of establishing an electric current path through the hot glass to heat the glass, generating an error signal which represents any departure of the resistance of the glass in that path when at the desired viscosity from the predetermined reference value, and continuously regulating the current flow through the glass to maintain the glass at the desired viscosity.

Claim 4

A method according to claim 1 in which the voltage and the current supplied to the path are sensed continuously, the signal indicative of the reciprocal of the current is multiplied continuously by the signal indicative of the voltage and the signal proportional to the resistance of the path is compared continuously with the reference signal.

Claim 5

An electrical control circuit for maintaining an electriCally resistive path at a desired temperature, including a voltage sensing device for connection across the path and operable to produce an indication of the voltage across the path, a current sensing device connected in series with the path and with a current regulating device operable to control the current supplied to the path, analogue circuits associated with the sensing devices for producing the product of the voltage with the reciprocal of the current, a comparator circuit having inputs connected to the output of one of the analogue circuits and to a reference signal generator and an error output connected to the current regulating device so as to regulate the current supply to the path in accordance with the path resistance as determined by the product of the voltage and the reciprocal of the current.

Claim 6

An electrical control circuit for maintaining an electriCally resistive path at a desired temperature, including a voltage sensing device for connection across the path and operable to produce an indication of the voltage across the path, a current sensing device connected in series with the path and with a current regulating device operable to control the current supplied to the path, analogue circuits associated with the sensing devices for producing the product of the voltage with the reciprocal of the current, a comparator circuit having inputs connected to the output of one of the analogue circuits and to a reference signal generator and an error output connected to the current regulating device so as to regulate the current supply to the path in accordance with the path resistance as determined by the product of the voltage and the reciprocal of the current.

Claim 7

A control circuit according to claim 4, wherein the current sensing device includes a solid state Hall effect device having an input connected in series with the resistive path, and being connected in the feedback loop of a high gain differential amplifier which is connected to a reference signal source to provide an analogue inverter, the output from the amplifier representing the reciprocal of the sensed current, and the voltage sensing device includes a second solid state Hall effect device connected as an analogue multiplier having a voltage input connected across the resistive path, a current input connected to the output from the differential amplifier and an output connected to the comparator in order to transmit thereto a signal indicative of the resistance of the path.

Claim 8

A control circuit according to claim 4, wherein the current regulating device is controlled by the output from a pulse generator.

Claim 9

A control circuit according to claim 4, wherein continuous indications are obtained of the voltage across and the current passing through the path.

Claim 10

A control circuit according to claim 4, wherein the error output from the comparator circuit is continuous.