Calibration of a plurality of excitation sources for an instrumentation system

DETAILED DESCRIPTION A calibration system for calibrating a plurality of excitation sources for an instrumentation system according to the present invention includes a single adjustable reference source with a single variable input for providing an adjustable reference signal to all of the excitation sources.
In this manner, calibration is performed once for a plurality of excitation channels, thereby simplifying the entire calibration procedure.
Furthermore, a single reference source and variable input substantially reduces cost since it is not necessary to include separate reference sources for each of the channels.
In the preferred embodiment, the adjustable reference source is a variable voltage device including a variable resistor or potentiometer for adjusting a reference voltage.
The variable voltage device includes a Zener diode having an adjustable input connected to a potentiometer, where the potentiometer is adjusted for controlling the adjustable input and thus the reference voltage across the Zener diode.
The reference voltage is applied to a plurality of current source circuits, each providing a current excitation signal on one or more corresponding channels of the instrumentation system.
Each of the current sources preferably includes an amplifier and transistor circuit for controlling the current through a precision resistor.
In particular, the amplifier is coupled as a voltage follower applying the reference voltage across the precision resistor, where the amplifier further controls the transistor for developing a calibrated current through the precision resistor.
Since the voltage reference signal is adjusted only once, all of the current excitation source outputs are simultaneously calibrated.
It is thus appreciated that the present invention substantially improves calibration of a plurality of excitation source channels by using a single calibration adjust circuit for all channels for simultaneous calibration.
The use of a single calibration circuit improves efficiency and reduces cost of the instrumentation system