Greenlee CMT-90 User manual

999 6756.1 REV 1 © 2005 Greenlee Textron Inc. 9/05
CMT-90
Clamp-on Meter
Medidor
con pinza
Contrôleur
numérique
à pinces
INSTRUCTION MANUAL
INSTRUCTION MANUAL
MANUAL DE INSTRUCCIONES
MANUEL D’INSTRUCTIONS
Read and understand all of the instructions and
safety information in this manual before
operating or servicing this tool.
Lea y entienda todas las instrucciones y la
información sobre seguridad que aparecen en
este manual, antes de manejar esta herramienta
o darle mantenimiento.
Lire attentivement et bien comprendre toutes les
instructions et les informations sur la sécurité de
ce manuel avant d‘utiliser ou de procéder à
l‘entretien de cet outil.

2
Description
The Greenlee CMT-90 Digital Clamp-on Meter is a hand-held testing device
with the following measurement capabilities: AC and DC voltage, AC current,
and resistance. It also verifies continuity. The CMT-90 is a true RMS-reading
meter.
This unit has data hold capability. It automatically determines measurement
function based on input.
The display automatically illuminates for easy viewing in dark areas.
Safety
Safety is essential in the use and maintenance of Greenlee tools and
equipment. This instruction manual and any markings on the tool provide
information for avoiding hazards and unsafe practices related to the use of
this tool. Observe all of the safety information provided.
Purpose of This Manual
This instruction manual is intended to familiarize all personnel with the safe
operation and maintenance procedures for the Greenlee CMT-90 Digital
Clamp-on Meter.
Keep this manual available to all personnel.
Replacement manuals are available upon request at no charge.
KEEP THIS MANUAL
All specifications are nominal and may change as design improvements occur.
Greenlee Textron Inc. shall not be liable for damages resulting from misapplication or
misuse of its products.
® Registered: The color green for electrical test instruments is a registered trademark of
Greenlee Textron Inc.
Do not discard this product or throw away!
For recycling information, go to www.greenlee.com.

3
CMT-90
Important Safety Information
This symbol is used to call your attention to hazards or unsafe
practices which could result in an injury or property damage. The
signal word, defined below, indicates the severity of the hazard. The
message after the signal word provides information for preventing or
avoiding the hazard.
SAFETY ALERT SYMBOL
Immediate hazards which, if not avoided, WILL result in severe injury
or death.
Hazards which, if not avoided, COULD result in severe injury or death.
Hazards or unsafe practices which, if not avoided, MAY result in injury
or property damage.
Read and understand this material before
operating or servicing this equipment. Failure to
understand how to safely operate this tool could
result in an accident causing serious injury or
death.

4
Important Safety Information
Electric shock hazard:
• Do not apply more than the rated voltage between any two input
terminals, or between any input terminal and earth ground.
• Do not contact the test lead tips or any uninsulated portion of the
accessory.
Failure to observe these warnings could result in severe injury or death.
Electric shock and fire hazard:
• Do not expose this unit to rain or moisture.
• Do not use the unit if it is wet or damaged.
• Use test leads or accessories that are appropriate for the application.
Refer to the category and voltage rating of the test lead or accessory.
• Inspect the test leads or accessory before use. They must be clean and
dry, and the insulation must be in good condition.
• Use this unit for the manufacturer’s intended purpose only, as
described in this manual. Any other use can impair the protection
provided by the unit.
Failure to observe these warnings could result in severe injury or death.
Electric shock hazard:
Contact with live circuits could result in severe
injury or death.

5
CMT-90
Important Safety Information
Electric shock hazard:
• Do not operate with the case or battery cover open.
• Before removing the case or battery cover, remove the test leads
(or jaw) from the circuit and shut off the unit.
Failure to observe these warnings could result in severe injury or death.
Electric shock hazard:
• Unless measuring voltage or current, shut off and lock out power. Make
sure that all capacitors are discharged. Voltage must not be present.
• Using this unit near equipment that generates electromagnetic
interference can result in unstable or inaccurate readings.
Failure to observe these warnings could result in severe injury or death.
Electric shock hazard:
• Do not attempt to repair this unit. It contains no user-serviceable parts.
• Do not expose the unit to extremes in temperature or high humidity.
Refer to “Specifications.”
• Do not connect to voltage for longer than 30 seconds.
Failure to observe these precautions may result in injury and can damage
the unit.
Electric shock hazard:
Do not use the meter to measure voltages in circuits that could be
damaged by the meter’s low input impedance (approximately 4 kΩ).
Failure to observe this precaution may result in injury and can damage the
unit.

6
Identification
1. Jaw
2. Lever
3. Display
4. Common (COM) input terminal
5. Volts or resistance (V-Ω) input terminal
6. ON/OFF/HOLD button
7. Sensor for automatic backlit display
Display Icons
8. Low battery indicator
9. DC measurement is selected
10. –Polarity indicator
11. AC measurement is selected
12. Automatic selection is active
13. HOLD Hold function is enabled
14. LoZi Low input impedance is active
15. VVoltage
16. AAmperes
17. Ohms
18. Continuity
19. OL Overload indicator
8
9
1
0
11
12
1
3
–
14
1
5
–
16
17
1
8
1
9
Symbols on the Unit
Warning—Read the instruction manual
Electric shock hazard
Double insulation
Battery
Recycle product in accordance with manufacturer’s directions
Note: Icons that
appear on the
display but are not
identified are not
used on this model.
1
2
3
4 5
6
7

7
CMT-90
*The crest factor is the ratio of the peak value to the RMS value; it is
represented by the Greek letter ξ.
AC Measurement
AC measurements are usually displayed as RMS (root mean squared) values.
Two methods of AC measurement are average-responding RMS calibrated
and true RMS-reading.
The average-responding RMS calibrated method takes the average value of
the input signal, multiplies it by 1.11, and displays the result. This method is
accurate if the input signal is a pure sine wave.
The true RMS-reading method uses internal circuitry to read the true RMS
value. This method is accurate, within the specified crest factor limitations,
whether the input signal is a pure sine wave, a square wave, sawtooth wave,
half wave or signal with harmonics. The ability to read true RMS provides
much more measurement versatility. The Greenlee CMT-90 is a true RMS
meter.
The Waveforms and Crest Factors table shows some typical AC signals and
their RMS values.
Waveforms and Crest Factors
Waveform
RMS Value 100 100 100 100
Rectified Value 90 100 87 64
Crest Factor* 1.414 1 1.73 2
(ξ)

8
Operation
2. Refer to “Typical Measurements”for specific measurement instructions.
3. Test the unit on a known functioning circuit or component of the type you
intend to measure.
•If the unit does not function as expected on a known functioning
circuit, replace the battery.
•If the unit still does not function as expected, send the unit to Greenlee
for repair. Refer to the instructions under the Warranty.
4. Take the reading from the circuit or component to be tested.
Note: Momentarily press the ON/OFF/HOLD button to hold the present
measurement on the display; momentarily press again to return to the normal
display mode. Press and hold to turn the unit off.
Priority Display Conditions
AC volts or Input at terminals is
1DC volts, 1.3 to 999.9 VAC
whichever 1.8 to 999.9 VDC
is greater –0.6 to –999.9 VDC
Input at terminals is
Resistance 0 to ∞Ω
2 and 0 to 0.9 VAC
continuity 0.2 to 1.4 VDC
–0.02 to –0.2 VDC
3 AC amps AC current through jaw is
0.6 to 600.0 A
Electric shock hazard:
Contact with live circuits could result in severe
injury or death.
1. The meter automatically selects the proper measurement according to
the following table.

9
CMT-90
Typical Measurements
Current Measurement—
Clamp Around Wire
Notes:
•Clamp the jaw around one conductor only.
•Close the jaw completely to ensure
accurate measurement.
•Center the wire in the jaw for highest
accuracy.
Current Measurement—
Clamp Around Line Splitter
Notes:
•The Greenlee 93-30 Line Splitter is divided.
One section renders amps; the other
renders amps multiplied by 10.
•Close the jaw completely to ensure
accurate measurement.
•Center the line splitter in the jaw for highest
accuracy.

10
Typical Measurements
Voltage Measurement
Resistance
Measurement
Continuity Check