OperatingBasics
12 P5205 Instruction Manual
Both ranges are rated for the maximum input limits, but youcan
obtain a useful measurement only if the volt age you apply is within
the specified limitsof the operating range.
Overrange Detection
Differential voltage outside the operating range will overdrive the
circuitry of the probe and distort the output signal . When this
differentialoverrange occurs, the probe detects the conditionand
lights the overrange indicator. With the Audible Overrange ON, the
probe will also emit an audible alarm .
Common-mode voltage greater than 1,000 VRMS can di stort the
output signal, but the probe will not indicate an overrange condition.
Common-Mode Rejection
The common-moderejection ratio (CMRR) is the specified ability of
P5205 probe to reject signals that are common to bot h inputs. More
precisely,CMRR is the ratio of the differential gain to the common-
mode gain. The higherthe ratio, the greater the ability of probe to
reject common-mode signals. For exact specificati ons,see pa ges15
and 17.
Common mode rejection decreases as the input frequency increases.
Figure 5 on page 18 is a plot of typical CMRR of the probe versus
input frequency. For example, if you apply a 60 Hz line voltage of
500 VP-Pt obot hi nput leads of the probe, the probe rejects the signal
by 80 dB (typical) and the signal appears as only a 50 mVP-P signal
on the oscilloscopescreen.
Tomaximize the rejection of common-mode signals, twistthe input
leads together as shown in Figure 3 on page 13, and do not use the
extensionleads.
Twistingthe Input Leads
Twisting the input leads as shown in Figure 3 helps to cancel noise
that is induced into the input leads and to i mprove the high-frequen-
cy response of the inputs. For the best response possible, do not use
the extensionleads.