Abstract In a system which continuously measures the composition, position or size of materials, the probe has a guard shield which is effective for continuous measurement. The measurement system includes a zero adjusting impedance connected with the variable probe impedance as two adjacent arms of a balanceable bridge. A span impedance is connected between the junction of the adjacent arms and a low impedance AC source. The buffer amplifier has its input connected across the span impedance so that changes in the input impedance of the amplifier do not change the operating point of the system. A guard shield amplifier has its input connected to the output of the buffer amplifier. The guard shield amplifier maintains the guard shield at the same potential as the voltage on the probe electrode continuously for all points of operation, without significantly changing the voltage.
A buffer amplifier comprising: a unity gain amplifier which includes: a high-gain amplifier, a second amplifier directly coupled to said high-gain amplifier, said second amplifier providing a substantially 100 per cent voltage feedback to said high-gain amplifier, the output to said unity gain amplifier being capacitatively bootstrapped to the input of said unity gain amplifier, said input acting as the input to said buffer amplifier, an emitter follower amplifier capacitatively coupled to the output of said unity gain amplifier to supply power to said unity gain amplifier from a source which is of the same A.C. potential as the output of said buffer amplifier, and a capacitative coupling between the output to said buffer amplifier and the input to said unity gain amplifier.
Claim 2
Dependent Claim
123 words
A buffer amplifier comprising: a unity gain amplifier which includes: a high-gain amplifier, a second amplifier directly coupled to said high-gain amplifier, said second amplifier providing a substantially 100 per cent voltage feedback to said high-gain amplifier, the output to said unity gain amplifier being capacitatively bootstrapped to the input of said unity gain amplifier, said input acting as the input to said buffer amplifier, an emitter follower amplifier capacitatively coupled to the output of said unity gain amplifier to supply power to said unity gain amplifier from a source which is of the same A.C. potential as the output of said buffer amplifier, and a capacitative coupling between the output to said buffer amplifier and the input to said unity gain amplifier.