General Tools and Instruments CMR35 - Manual (Page 11)

•
WARNING
•
To avoid exposing yourself to a harmful or a fatal voltage and damaging the
transmitter, make sure that the AC voltage or current whose frequency you are
measuring has an amplitude of less than 600V.
As in current measurement mode, the CMR35T automatically chooses the narrowest
measurement range that includes the tested value. The six available full-scale ranges
are 0 to 5Hz, 0 to 50Hz, 0 to 500Hz, 0 to 5kHz, 0 to 50kHz, and 0 to 100kHz.
Read the measured value once it stabilizes. When you have finished making frequency
measurements, move the function switch to the OFF position.
MAKING RELATIVE MEASUREMENTS
Pressing the transmitter’s REL./SEL. button (callout 7/8 of Fig. 1) while the transmitter is
measuring AC or DC current flow lights the
{
REL symbol on the top line of the
transmitter’s display (see Fig. 2). When this mode—called relative measurement
mode—is activated, the transmitter will display the difference between the values of
successive inputs.
For example, if the transmitter was measuring 10 Amperes when the REL./SEL. button
is pressed and then is connected to a line carrying 15 Amps, the transmitter’s display
will read 5A (the difference between 15A and 10A). If the transmitter’s clamp or probes
are then switched to a line carrying 50 Amps, the display will read 40 Amps (50A minus
the first input value, 10A). A series of relative measurements can be carried out
indefinitely.
Pressing the REL./SEL. button when the transmitter is operating in AC or DC current
measurement mode also deactivates the autoranging function. This causes the AUTO
RANGE text to disappear from the transmitter’s display and sets the transmitter’s
measurement range to a fixed value—the lowest full-scale value that can accommodate
the value being measured when the REL./SEL. button was last pressed (10A in the
above example). If the relative value exceeds this fixed value, the display will read “OL”.
To exit relative measurement mode, press the REL./SEL. button again to make the
{
REL
symbol disappear from the top line of the transmitter’s display. To reactivate the
autoranging function, move the function switch to the OFF position, and then to the
position corresponding to the next type of measurement you wish to make.
The REL./SEL. button also has a secondary function; zeroing the transmitter’s display in
DC current measurement mode. If the display shows a residual reading before the jaws
of the clamp are placed around a conductor or before the transmitter’s leads are
connected to a circuit, pressing the REL./SEL. button will “zero out” the display and
deactivate the autoranging function.
As explained earlier, to exit relative measurement mode press the REL./SEL. button
again to make the
{
REL symbol symbol disappear. To reactivate autoranging, move the
function switch first to the OFF position and then to the desired measurement position.
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CMR35 Manual FINAL4_020911:awb 2/9/11 11:54 AM Page 11