B&K Precision 1856D - Manual - Manual (Page 21)

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DO NOT USE A 10:1 PROBE WITH THE INPUT C. THESE PROBES ARE
DESIGNED WITH A 10:1 ATTENUATION FOR AN INSTRUMENT WITH AN
INPUT RESISTANCE OF 1 M

. THE 50

TERMINATION OF INPUT C WOULD
RESULT IN UNACCEPTABLY HIGH ATTENUATION.
5-3. Line Frequency Measurements
When making line frequency measurements, use of the LOW PASS FILTER, the
ATTENUATOR, and/or the 10:1 probe is recommended.
WARNING
USE CAUTION WHEN MEASURING THE LINE FREQUENCY OF AN AC
OUTLET. USE THE PROBE TIP ONLY, AND MEASURE BOTH SIDES OF THE
LINE. THE NEUTRAL SIDE WILL GIVE A ZERO READING AND THE HOT SIDE
WILL PROVIDE THE DESIRED MEASUREMENT. DO NOT USE THE "GROUND"
LEAD OF THE PROBE. REMEMBER THAT THE CHASSIS OF THE COUNTER
AND THE “GROUND” LEAD OF THE PROBE ARE ALREADY AT EARTH
GROUND (VIA THE 3-WIRE POWER CORD OF THE INSTRUMENT). TOUCHING
THE
“GROUND" LEAD TO THE 'HOT" SIDE OF THE LINE WOULD PLACE A
DIRECT SHORT ON THE POWER LINE THROUGH THE PROBE CABLE,
RESULTING IN A BIG SPARK, DAMAGE TO THE PROBE CABLE, AND
POSSIBLE INJURY TO THE USER.