Loz Voltage Measurements; Low Pass Filter (Vfd) Ac Voltage Measurements - FLIR CM94 User Manual

5
Meter Operation

5.8 LoZ Voltage Measurements

In LoZ mode, the input impedance increases quickly from the initial 2.5kΩ to a few hun-
dred kΩ's on high voltage signals. Peak initial load current, while testing 1000 V AC for ex-
ample, can be as high as 566 mA (1000 V x 1.414 / 2.5kΩ), decreasing to roughly 3.37
mA (1000 V x 1.414 / 420kΩ) within a fraction of a second. Do not use LoZ mode on cir-
cuits that could be damaged by such low input impedance. Use the standard high input im-
pedance voltage modes to minimize loading on such circuits.
Use caution when the measured voltage is greater than 30V DC or AC rms.
LoZ Voltage measurements eliminate the affects of 'ghost' voltages. The pro-
cedure for taking LoZ Voltage measurements is essentially the same as for
taking standard Voltage measurements, the only difference is that for LoZ
Voltage measurements you select the LoZ rotary switch position and you must
take into consideration the effect low impedance will have on circuitry that you
test (read Warning statement above). Refer to the previous section for other
Voltage measurement details.
When you turn the rotary dial to the LoZ position, the display will show 'auto'
indicating that the CM94 will automatically detect the measured signal as AC
or DC.

5.9 Low Pass Filter (VFD) AC Voltage Measurements

Use caution when the measured voltage is greater than 30V DC or AC rms.
Select the VFD mode using the rotary selector switch.
The VFD feature eliminates high frequency noise in AC voltage measure-
ments by means of a low pass filter. The VFD mode is designed for variable
frequency drive measurements. The VFD icon will appear on the display in
this mode. The procedure for taking VFD Voltage measurements is identical
to the procedure for taking standard Voltage measurements. Refer to the pre-
vious sections for Voltage measurement details.
#NAS100019; r. AC/59959/59961; en-US
WARNING
CAUTION
CAUTION
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