US 4,061,891 AGranted

Test instrument for determining apparent power consumption and ground faults in various portions of a distributed-load, constant voltage audio distribution system

OwnerWayne A. Pommerinventor

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Abstract

To determine apparent power consumption in a distributed-load, constant voltage audio distribution system, a test instrument is provided which is substituted for the amplifier in the system during the test. A constant, known AC test voltage at a convenient audio frequency is applied to the distribution system or a portion thereof. The resultant AC current passing through the distribution system is measured and read on a meter calibrated directly in watts. The apparent power consumed in the system is directly proportional to the current. The instrument is provided with an internal audio frequency oscillator as a test signal source with a provision for bypassing it so that an external oscillator may be utilized. The oscillator signal is processed by a voltage controlled amplifier and a power amplifier wherein the signal level is controlled. The processed test signal is applied to the system under test. The voltage across a resistance in series with the tested circuit is monitored through an isolating buffer. A summing amplifier connected to the buffer through an AC to DC converter has additional variable DC inputs to permit the zero adjustment and load nulling on the indicating meter connected to the output of the summing amplifier. An overload indication circuit monitors the signal applied to the meter to provide a signal indicating that another value of resistance in series with the tested circuit should be selected. A feed back loop provides a signal controlling the level of the test signal.

Claims18

Dependent claims

A test instrument for determining apparent power consumption in various portions of a distributed-load, constant-voltage audio distribution system, comprising:

a. a controlled output amplifier having an input for receiving an audio input signal of a frequency at which the apparent power consumption is to be tested, a control signal, input, and an output which controlled amplifier produces an output signal at the test frequency of a voltage dependent on the magnitude of the signal received at the control signal input;
b. a resistance;
c. means for connecting the resistance to the output of the controlled amplifier;
d. means for connecting the resistance to that portion of the distributed-load, constant-voltage audio distribution system to be tested so that a test signal is applied to the portion of the system to be tested and the current that passes through the resistance is substantially equivalent to that which passes through that portion of the system to be tested;
e. means for supplying a reference voltage signal having a magnitude corresponding to the voltage at which the apparent power consumption is to be determined;
f. means, having inputs connected to the reference voltage supply means and the audio distribution system connection means and an output which is connected to the control signal input of the controlled amplifier, for producing an error signal at the output so that a test signal of a voltage corresponding to the voltage at which the apparent power consumption is to be determined is applied to the circuit under test at the audio distribution system connection means;
g. means connectable across the resistance for producing a signal having a magnitude indicative of the amount of current passing through the resistance;
and
h. means connected to the current magnitude signal means for indicating the magnitude of the current passing through the resistance which indication is indicative of the apparent power consumed by the tested system.

6 more elements

A test instrument for determining the apparent power consumption in various portions of a distributed-load, constant-voltage audio distribution system, comprising:

a. a controlled output amplifier having a voltage controlled amplifier having an input for receiving an audio input signal of a frequency at which the apparent power consumption is to be tested and a control signal input;
a power amplifier having its input connected to the output of the voltage controlled amplifier;
and an isolation transformer having its primary connection to the output of the power amplifier so that an isolated audio frequency signal is produced at its secondary with a voltage magnitude that is dependent on the magnitude of a signal received at the control input of the voltage controlled amplifier.
b. a plurality of resistances corresponding to different levels of apparent power consumption;
c. means for selectively connecting the resistances between that portion of the distributed-load, constant-voltage distribution system to be tested and the secondary of the isolation transformer so that a test signal is applied to that portion under test and the current that passes through the resistance is substantially equivalent to that which passes through that portion of the system being tested;
d. means for supplying a reference voltage signal having a magnitude corresponding to the voltage at which the apparent power consumption is to be determined including a resistance having a plurality of taps proportional to different voltage levels utilized in such systems to form a voltage divider;
e. an error signal generator having a buffer having its input connected to the audio distribution system connection means to monitor the voltage level of the audio frequency test signal applied to that portion of the circuit being tested and to isolate it and minimize the effect of the monitoring;
an RMS converter connected to the output of the buffer to generate a DC signal having a magnitude which corresponds to the magnitude of the test signal;
a differential amplifier having one input connected to the output of the RMS converter and one input connected to the reference voltage supply means producing an output signal having a magnitude which corresponds to the amount by which the test signal varies from the desired voltage;
and an integrator having its input connected to the output of the differential amplifier and its output connected to the control signal input of the voltage controlled amplifier to rapidly adjust the voltage level of the test signal to a desired level;
f. a current signal generator having a buffer having its input connected to the connection means to monitor the current through the resistance to isolate the resistance and minimize the effect of monitoring;
an RMS converter having its input connected to the output of the buffer;
a first means for supplying a variable DC voltage;
a second means for supplying a variable DC voltage;
a summing amplifier having a first input connected to the output of the RMS-converter, a second input connected to the first DC supply means to provide a signal level adjustment, and a third input connected to the second DC supply means to provide a load nulling capability;
g. an indicator connected to the output of the summing amplifier to indicate the apparent power consumed by the portion of the system under test which is directly related to the current through the resistance.

13 more elements

Dependencies are inferred from the claim text.