A-M Systems
131 Business Park Loop, P.O. Box 850 Carlsborg, Wa 98324
Telophone: 800-426-1306 * 360-683-8300 * FAX: 360-683-3525
E-mail: [email protected] * Website: http://www.a-msystems.com
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a measure of the electrode impedance. The output of A1 is then fed to A100, whose gain
is set at x0.01 by relay RL11. The signal next passes through A 101 (x10 gain), A102
(unity gain) and finally through A103, which has a unity gain set by RL14 through disabling
the gain selection circuit.
The current source consists of several parts. A stable timer (A300) produces a 15 V p-p
square wave at 1 kHz that is attenuated by a 5K potentiometer. The attenuated square-
wave is applied to a bandpass filter (A301) which passes the center frequency of the
square-wave but rejects the harmonics, resulting in a 1 kHz sine wave which is scaled to 2
V p-p by a 5K potentiometer. The 2 V p-p sine wave (TP300) is applied to an active
current source (A400 and A401), which converts the sine wave voltage to a sine wave
current of 0.1 µA p-p at 1 kHz. The calibrated current source is connected to relay RL11,
which switches the current to the electrode leads. The Capacity Compensation feedback
circuit (A402) reduces the amount of capacitance across the electrodes allowing only the
resistive component of the electrode to be measured.
Component Modules
Differential Amplifier
The Differential Amplifiers (A100, A200) make the transformation from a differential signal
to a single-ended signal. T102 and T202 are adjusted to balance this stage and
maximize the common-mode rejection.
Low Frequency Cut-Off Filter
The Low Frequency Cut-Off Filters (A101, A201) are second-order Butterworth high-pass
filters with selectable cut-off points.
Notch Filter
The Notch Filters (A102, A202) are tuned to the line frequency. The circuit consists of a
twin-T network in a feedback loop with an operational amplifier.
High Frequency Cut-Off Filter
The High Frequency Cut-Off Filters (A103, A203) are second-order Butterworth low-pass
filters with selectable cut-off points.
Summary of Contents for 1800
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