Installation, Operation and Service Manual
LKP Series
© 2016 DynAmp, LLC
Page 20
041749 K
operating at its highest operating level, take two sets of readings, the first set taken
immediately (to verify no condition exists that may cause damage to the LKP Metering
Unit), and the second set after a 24-hour period of time (to thermally stabilize the head).
Proceed as follows:
A.) The dc voltage range may be as high as 75 Vdc (see “D” below). Make certain the
voltmeter being used is set to measure average dc volts in this range.
B.) The measured bus and all other high current buses in the vicinity (or in the facility)
should be operating at or near their highest levels. Note: All magnetic field sources
will affect the channel voltage readings.
C.) Make a photocopy of table “Form for Recording Channel Voltage Measurements”.
The initial readings are made as instructed on the form, and are recorded in the
individual blocks. Refer to the head schematic drawing in the back of the manual,
which graphically show the channel locations on the head.
D.) Excluding the effects of external magnetic sources and assuming a full rated bus
current, each channel is expected (by calculation) to measure approximately as
shown in Table 5.2 below. In practice, channel readings will be different depending
on the operating current level, ambient temperature, and cable length. The table
shows full-scale voltages with a well balanced channel distribution, and with a
maximum unbalance of the channel loading of 130% (assuming one half of the head
is operating at 30% above nominal rating and the other half is at 30% below nominal).
A channel failure will usually be indicated by either a full-off (near zero), half-on (35-
38V) or full-on (70-75V) condition.
E.) If any of the channel readings do indicate trouble, refer to Theory of Operations and
Maintenance & Spare Parts sections and resolve the problem; then proceed with
"Magnetic Centering".
TABLE 5.2 CALCULATED CHANNEL VOLTAGE
Channel voltage @ full scale current (Volts)
Model
Well balanced chan.
loading @ 25°C
130% unbalance chan.
loading @ 25°C ambient
130% unbalance chan.
loading @ 55°C ambient
180
27
36
41
300
37
48
58
400
40
55
62
Note 1.
Low Readings: A very low amplifier output voltage may be normal for certain
channels; however, ripple can be as high as 3 V on a non-operating (full-off) channel.
Thus, a very low reading (i.e., 1 V to 3 V, should be suspected as a possible problem;
subsequent head movement or other magnetic change may show that the channel is good.
Note 2.
High Readings: The maximum allowable channel output relates to the maximum
heat dissipation that the channel can safely handle. A reading near the maximum 130%
unbalance voltage makes a change in head position highly desirable. A reading at or
exceeding the maximum unbalanced voltage makes a head position change necessary. A
reading of 70-75 V indicates a full-on channel condition or a blown channel fuse, and
requires immediate action to resolve the problem. A reading of 35-38 V when immediately
adjacent channels are significantly different may indicate that one of the two SCRs in the
channel has failed.
