Greenlee CM-900 User manual

999 4754.4 © 2003 Greenlee Textron 3/03
CM-900 • CM-950
Digital Clamp-on
Meters
Medidores digitales
con pinza
Multimètres
numériques 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 estas
herramientas o darles 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 CM-900 and CM-950 Digital Clamp-on Meters are hand-held testing devices with
the following measurement capabilities: AC and DC voltage, AC and DC current, frequency, and
resistance. They also verify continuity. The CM-950 is a true RMS reading meter.
Specialized functions and capabilities include:
• Auto ranging
• Backlit display
• Auto power off
• Data hold
• MIN MAX hold
• Peak hold
• 42-segment bar graph
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 Greenlee CM-900 and CM-950 Digital Clamp-on Meters.
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 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.

CM-900 • CM-950
3
Important Safety Information
Read and understand this material before operating or servicing
this equipment. Failure to understand how to safely operate this
tool can result in an accident causing serious injury or death.
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.

4
Important Safety Information
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 can result in severe injury or death.
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 can result in severe injury or death.
Electric shock hazard:
Contact with live circuits can result in severe injury or death.

CM-900 • CM-950
5
Important Safety Information
• 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 can result in severe injury or death.
• 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.”
Failure to observe these precautions can result in injury and can damage the unit.
Do not change the measurement function while the test leads are connected to a
component or circuit.
Failure to observe this precaution can result in injury and can damage the unit.
• Unless measuring voltage, current, or frequency, 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.

6
Identification
1. Jaw
2. Lever
3. Backlight button
4. MIN MAX button
5. Common (COM) input terminal
6. Volts or resistance (V-Ω) input terminal
7. PEAK button
8. ZERO button
9. Display
10. Selector
11. HOLD button
Display Icons
12. Low battery indicator
13. REL Status of DC current ZERO function
14. MIN MIN Hold function is enabled
15. –Polarity indicator for numeric display
16. MAX MAX Hold function is enabled
17. Hold function is enabled
18. DC measurement is selected
19. AC measurement is selected
20. kHz Kilohertz
21. MHz Megahertz
22. Volts Voltage
23. Amps Amperes
24. Ohms
25. Continuity
26. TRMS True RMS (CM-950 only)
27. PMAX MAX PEAK Hold function is enabled.
28. PMIN MIN PEAK Hold function is enabled.
29. –Polarity indicator for bar graph
30. Bar graph element
31. Overload indicator for bar graph
32. OL. Overload indicator for numeric display
Symbols on the Unit
Warning—Read the
instruction manual
Double insulation
Battery
1
2
3
4
5
10
11
9
8
7
6
12
13–14
15
16
17
26–28
18–25
3029
31
32

CM-900 • CM-950
7
Using the Features
•
Press to backlight the display. Press again to turn off. The backlight automatically shuts off
after approximately 1 minute.
•HOLD Button
Press momentarily to hold the present value on the display. Press again to return to normal
mode.
•Auto Power Off
The unit automatically shuts off after approximately 30 minutes of inactivity.
To disable this feature, press PEAK, MIN MAX, or while turning the meter on.
•MIN MAX Button
Press momentarily to begin recording the minimum and maximum values of input. Press
momentarily to cycle through the display modes as shown in the table below. The meter uses
its highest voltage or current range for this feature.
Press and hold to exit this mode.
•PEAK Button
Press momentarily to begin recording the minimum and maximum peak values of AC inputs.
Press momentarily to cycle through the display modes as shown in the table below. The meter
uses its highest voltage or current range for this feature.
Icon Display
MAX Maximum recorded value
MIN Minimum recorded value
MAX (flashing) Present measured value
MIN
Icon Display
PMAX Maximum recorded peak value
PMIN Minimum recorded peak value
Press and hold to exit this mode. “CAL”appears briefly on the display as internal circuitry is
reset.
•ZERO Button
Press momentarily to compensate for the residual magnetism in the jaw. “REL”appears on
the display. Press momentarily again to display the uncompensated measurement. The stored
offset value is retained. “REL”will flash. Press and hold to clear the stored offset value and
return to uncompensated measurement.
Repeat the procedure after changing DC current ranges.

8
Waveform
RMS Value 100 100 100 100
Average Value 90 100 87 64
Crest Factor* 1.414 1 1.73 2
(ξ)
AC Measurement
AC measurements are usually displayed as RMS (root mean square) values. The RMS value is
equal to the value of a DC waveform, which would deliver the same power if it replaced the time-
varying waveform. Two AC measurement methods are average-responding RMS calibrated and
true RMS-reading.
The average-responding RMS calibrated method takes the average value of the input signal after
full wave rectification, multiplies it by 1.11, and displays the result. This method is accurate if the
input signal is a pure sine wave. The Greenlee CM-900 is an average-responding meter.
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, square wave, triangle wave, half wave, or signal with harmonics. The ability to read true
RMS provides much more measurement versatility. The Greenlee CM-950 is a true RMS meter.
The Waveforms and Crest Factors table shows some typical AC signals and their RMS values.
Waveforms and Crest Factors
*The crest factor is the ratio of the peak value to the RMS value; it is represented by the Greek
letter ξ.

CM-900 • CM-950
9
1. Set the selector according to the Settings Table. For DC current, start with the 600 A range.
2. Refer to “Typical Measurements”for specific measurement instructions.
3. Test the unit on a known functioning circuit or component.
•If the unit does not function as expected on a known functioning circuit, replace the
battery (or batteries).
•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.
5. If it is a DC current reading, remove the clamp from the circuit and press the ZERO button.
Clamp the jaw around the circuit again to measure the actual DC current.
If the resolution is not satisfactory on the 600 A range, remove the meter from the
conductor and switch to the 400 A range. Repeat steps 4 and 5.
Settings Table
Electric shock hazard:
Contact with live circuits can result in severe injury or death.
Operation
To measure set the selector connect the and connect the
this value …to this symbol …red lead to …black lead to …
Continuity* V-ΩCOM
Resistance V-ΩCOM
DC Voltage V-ΩCOM
AC Voltage V-ΩCOM
DC Current (600 A max.) Remove lead Remove lead
DC Current (400 A max.) Remove lead Remove lead
AC Current (600 A max.) Remove lead Remove lead
Frequency Hz Remove lead Remove lead
*Tone sounds if the measured resistance is less than approximately 30 Ω.

10
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.
Voltage Measurement
Note: For DC measurements, current
flowing through the jaw in the direction
indicated by the arrow produces a positive
reading. Position the jaw for a positive
reading for highest accuracy.