UEi Test Instruments DL235 - Manual (Page 9)

DL235-MAN P. 8
Distribution Transformers
You can measure excessive current, load balance between phases, True
RMS and frequency of neutral current. True RMS measurement yields
the effective value.
1. Press the “ON/OFF” push-button to turn on the meter.
2. Clamp around the phase wire of the transformer. Be sure the
clamp jaws are securely closed, or measurements will not
be accurate.
3. Observe the display for True RMS current flow.
4. Repeat your measurement for each phase to observe balance.
Unbalanced phases cause large neutral currents flow.
5. Clamp around the neutral wire.
6. Observe the display for True RMS current flow. Any significant
flow, with balanced phases, indicates the presence of
harmonic currents.
7. Press the “Hz” push-button to measure the frequency of neutral
wire. Reading indicates the frequency of the dominant current
flow (in case of harmonic current flow, 180 Hz reading in
a 60 Hz system).
8. To freeze the digital display, press the “HOLD” push-button.
9. To measure half-cycle peak amperes, press the “SOFT CREST”
push-button twice (“PEAK” displayed). A crest factor other than
1.414 is an indication of harmonic current flow.
10. To record readings and to view minimum, maximum, and average
values, press the “MIN/MAX” push-button.
11. To clear “RECORD”, press the “MIN/MAX” push-button for
2 seconds.
Adjustable Speed Motor Controllers
You can measure input current, output current and frequency of the
adjustable speed motor controllers. The output current frequency is
used to calculate the rotating speed of the motor, while input current
f r e q u e n cy is used to measure the frequency of the power line. The
f r e q u e n cy of the output current is important because the voltage frequency
is often meaningless for the calculations of motor controller speed.
1. Press the “ON/OFF” push-button to turn on the meter.
2. Clamp around an input or output phase (as required), and run
motor at desired speed. Be sure the clamp jaws are securely
closed, or measurements will not be accurate.
3. Observe the display for True RMS current flow.
4. Measure an output phase of the motor controller and use “Hz”
mode to measure frequency. Nominal motor speed is calculated
from RPM = 120 F/P, where F is the frequency measured, and P
is the number of motor poles.
5. To record readings and to view readings, press the
“MIN/MAX” push-button.
6. To clear “RECORD”, press the “MIN/MAX” push-button for
2 seconds.
M a i n t e n a n c e
Periodic Service
WARNING!
Repair and service of this instrument is to be performed by qualified
personnel only. Improper repair or service could result in physical
degradation of the meter. This could alter the protection from
electrical shock and personal injury this meter provides to the
operator. Perform only those maintenance tasks that you are
qualified to do.
These guidelines will help you attain long and reliable service from
your meter:
• Calibrate your meter annually to ensure it meets original
performance specifications
• Keep your meter dry. If it gets wet, wipe dry immediately.
Liquids can degrade electronic circuits
• Whenever practical, keep the meter away from dust and
dirt that can cause premature wear
• Although your meter is built to withstand the rigors of daily
use, it can be damaged by severe impacts. Use reasonable
caution when using and storing the meter
Cleaning
Periodically clean your meter’s case using a damp cloth. DO NOT use
abrasive, flammable liquids, cleaning solvents, or strong detergents as
they may damage the finish, impair safety, or affect the reliability of the
structural components.
Battery Replacement
Always use a fresh replacement battery of the specified size and type.
Immediately remove the old or weak battery from the meter and
dispose of it in accordance with your local disposal regulations. Batteries
can leak chemicals that corrode electronic circuits. If your meter is not
going to be used for a month or more, remove and store the battery in
a place that will not allow leakage to damage other materials.
WARNING!
Disconnect the test leads from the circuit under test and from the meter
prior to removing or installing batteries.
To install a new battery, follow these procedures:
1. Turn off the meter.
2. Place meter face down on a clean cloth.
3. Remove the screws from the rear case.
4. Separate the two halves to expose the battery.
5. Remove and discard the old battery. Always dispose of old batteries
promptly in a manner with local disposal regulations.