Wide-range resistance monitoring apparatus and method

Apparatus for monitoring the resistance between first and second bodies, comprising:

• comparing means, electrically connected to said first and second bodies, for inducing current to flow between said first and second bodies and for producing an output signal whenever the magnitude of said current flow exceeds a reference level;
• switching means, operatively connected to said comparing means and connected to receive a periodic control signal, for alternating said reference level between first and second values in response to said control signal;
• and
• indicator means, connected to receive said output and control signals, for providing a first indication when said current flow is less than said first value and for providing a second indication when said current flow exceeds said second value, said indicator means including:
• a first transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base connected to receive said output signal, said collector being connected to receive said control signal;
• a second transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to said first transistor collector;
• and
• a first light emitting diode being connected between a supply voltage and said second transistor collector;
• a third transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to receive said control signal, said collector being connected to receive said output signal;
• a fourth transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to said third transistor collector;
• and
• a third light emitting diode being connected between a supply voltage and said fourth transistor collector.

Apparatus for monitoring the resistance between first and second bodies, comprising:

• comparing means, electrically connected to said first and second bodies, for inducing current to flow between said first and second bodies and for producing an output signal whenever the magnitude of said current flow exceeds a reference level;
• switching means, operatively connected to said comparing means and connected to receive a periodic control signal, for alternating said reference level between first and second values in response to said control signal;
• and
• indicator means, connected to receive said output and control signals, for providing a first indication when said current flow is less than said first value and for providing a second indication when said current flow exceeds said second value, wherein said indicator means includes:
• a first transistor having a base, and emitter and a collector, said emitter being connected to ground potential, said base connected to receive said output signal, said collector being connected to receive said control signal;
• a second transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to said first transistor collector;
• and
• a first light emitting diode being connected between a supply voltage and said second transistor collector;
• a further transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to the collectors of said first and third transistors, said collector being connected to said supply voltage;
• and
• a further light emitting diode being connected between said further transistor collector and emitter.

Apparatus for monitoring the resistance between first and second bodies, comprising:

• comparing means, electrically connected to said first and second bodies, for inducing current to flow between said first and second bodies and for producing an output signal whenever the magnitude of said current flow exceeds a reference level;
• switching means, operatively connected to said comparing means and connected to receive a periodic control signal, for alternating said reference level between first and second values in response to said control signal;
• and
• indicator means, connected to receive said output and control signals, for providing a first indication when said current flow is less than said first value and for providing a second indication when said current flow exceeds said second value, wherein said indicator means includes:
• a first transistor having a base, and emitter and a collector, said emitter being connected to ground potential, said base connected to receive said output signal, said collector being connected to receive said control signal;
• a second transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to said first transistor collector;
• and
• a first light emitting diode being connected between a supply voltage and said second transistor collector;
• a further transistor having a base, an emitter and a collector, said emitter being connected to ground potential, said base being connected to said first transistor collector, said collector being connected to said supply voltage;
• and
• a further light emitting diode being connected between said further transistor collector and emitter.

Apparatus for monitoring the resistance between first and second bodies, comprising:

• comparing means, electrically connected to said first and second bodies, for inducing current to flow between said first and second bodies and for producing an output signal whenever the magnitude of said current to flow exceeds a reference level;
• switching means, operatively connected to said comparing means and connected to receive a periodic control signal, for alternating said reference level between first and second values in response to said control signal;
• and
• indicator means, connected to receive said output and control signals, for providing a first indication when said current flow is less than said first value and for providing a second indication when said current flow exceeds said second value, wherein:
• said switching means sets said reference level to said first value when said control signal is present and sets said reference level to said second value when said control signal is not present;
• and
• said indicator means includes:
• means for producing an acoustical output in response to an electrical signal applied thereto;
• and
• means, connected to receive said control and output signals and electrically connected to said acoustical output producing means, for applying an electrical signal to said acoustic output producing means whenever either (a) said output signal is present and said control signal is not present, or (b) said output signal is not present and said control signal is present.

An apparatus for monitoring the electrical resistance between a body and ground potential, said apparatus comprising:

• operational amplifier means having first and second input terminals and an output terminal for generating an output signal at its output terminal in response to the relative levels present on its first and second input terminals;
• a resistive element electrically connected at one end to said body and electrically connected at its other end to said operational amplifier first input terminal;
• means for applying a fixed reference level to said operational amplifier second input terminal;
• switching means, operatively connected to said operational amplifier, for alternately connecting a first resistance and a second resistance between said operational amplifier output terminal and first input terminal;
• and
• indicating means, connected to said operational amplifier output terminal, for providing an indication in response to said operational amplifier output signal, said indicating means (a) providing a first indication whenever the resistance between said body and ground potential is less than a value set by said first resistance, (b) providing a second indication whenever the resistance between said body and ground potential is greater than a value set by said second resistance, and (a) providing a third indication whenever the resistance between said body and ground potential is between said first-mentioned and second-mentioned values.

An apparatus for monitoring the electrical resistance between a work surface and ground potential, said apparatus comprising:

• a lead electrically connected at one end to said work surface and having another end;
• operational amplifier means having first and second input terminals and an output terminal for generating an output signal at its output terminal in response to the relative levels present on its first and second input terminals, said first input terminal being electrically connected to the other end of said lead;
• means for applying a fixed reference level to said operational amplifier second input terminal;
• switching means, operatively connected to said operational amplifier, for alternately connecting a first resistance and a second resistance between said operational amplifier output terminal and first input terminal, said first and second resistances being a function of the upper and lower limits of a preset resistance range;
• a further operational amplifier having first and second input terminals and an output terminal, said first input terminal being connected to the output terminal of said first-mentioned operational amplifier;
• means for applying a further, fixed reference level to said further operational amplifier second input terminal;
• and
• indicating means, connected to said further operational amplifier output terminal, for providing an indication whenever the resistance between said work surface and ground potential is less than the lower limit of said preset resistance range, and whenever the resistance between said work surface and ground potential is greater than the upper limit of said preset resistance range.