A
Considerations For Operating In Constant Resistance Mode
The Agilent Electronic Loads implement Constant Resistance. (CR) mode by using either the CV circuits or CC circuits to regulate the input. The low range is regulated with the CV circuits, using the input current monitor as the reference. Therefore, resistance is described by the formula
V
= R
I
in which input current I is the reference, and voltage at the input terminals, V, is the parameter controlled to determine the resistance of the load.
The middle and high ranges are regulated with the CC circuits, using the input voltage monitor as the reference. Resistance is described by the formula
I 1
=
V R
in which input voltage V is the reference, and current through the input terminals, I, is the parameter controlled to determine the resistance of the load. The reciprocal of resistance, 1/R, is conductance, G. Therefore, the two highest ranges are best thought of as constant conductance ranges, with the CC circuit used to control conductance . This affects how the specified accuracy offset errors (in siemens or 1/ohms, formerly mhos) relate to programmed values (in ohms).
Any offset voltages in the op amps that comprise the load’s regulator circuits become errors at the input terminals of the load. In both CV and CC modes the offset is constant across the specified operating range, and can be accounted for during calibration.
The effects of offsets on CR mode accuracy are specified as
G =
I
V
the effect of an offset in current (I) on conductance (G) is greater at low input voltages and less for large input voltages.
The electronic load designs are optimized for
By contrast, a