Installation, Operation and Service Manual
LKP Series
© 2016 DynAmp, LLC
Page 26
041749 K
(referred to as a 4-channel assembly). A 4-channel system is used here as an illustration
to simplify the drawing and explanation.
A magnetic null detector (sensor), high-gain current amplifier, and feedback coil are
combined to form one channel, or current feedback loop. The function of each current loop
(current I
1
, I
2
, I
3
, or I
4
) is to maintain a state of zero flux in its related segment of the iron
core. A burden shunt placed in series with the total current (I
t
), develops an output voltage
E
o
, proportional to I
t
. The common side of the shunt is returned to the four high-gain
current amplifiers.
Since the bus current is directly proportional to the total current I
t
by a ratio of 5000:1, the
bus current can be measured accurately by summing the independent feedback currents (I
t
= I
1
+ I
2
+ I
3
+ I
4
). Therefore, the bus current is equal to 5000I
t
. Moving the Measuring
Head with respect to the bus will cause the values of the individual feedback currents to
change but will not affect the total current nor the accuracy of the measurement.
6.4 CIRCUIT FUNCTIONS
For the following discussion refer to the “High Range Module Schematic” and system
schematic drawings as appropriate. These drawings are located in the back of the manual.
Before discussing the various circuit functions, a general description of the Metering Unit
will be helpful. A Metering Unit may consist of one or more modular units. Each modular
unit contains the necessary circuitry for four channels of amplification. The Metering Unit
also contains one main power transformer, circuit breaker, and the resistors or shunts to
develop output voltages. A 4-channel system is used here as an illustration to simplify the
explanation.
Figure 6.2 Functional Diagram of Four-Channel
System
