2.7.2 Input Connections
The rear panel IivPIJT connector is a Teflon-insulated recep-
tacle intended for all input signals to the Model 617. As
shown in Figure 2-3, the center terminal is high, the inner ring
or shield is low, and the outer shield is connected to instru-
ment chassis ground. In the guarded mode, the inner shield is
driven at guard potential, while the Outer shield is chassis
ground.
NOTE
The input connector must be kept clean to main-
tain high input impedance.
The supplied Model 6011 input cable is designed to mate with
the input connector. The other end of the Model 6011 is ter-
minated with three alligator clips. Input high is color coded in
red, input low is colored black, and chassis ground is color
coded in green. Keep in mind that these connections are for
the unguarded mode. In the guarded mode, red is high, black
is guard, and green is chassis ground. The COM binding post
provides a connection to input low through loOn for use in
the guarded mode.
GROUND
GROUND
mm
A. UNGUARDED 6. GUARDED
I”, ii GUARD OFF)
W, R GUARD ON,
Figure 2-3. Input Connector Configuration
NOTE
It is recommended that zero check be enabled
when connecting or disconnecting input signals.
WARNING
The maximum common-mode input
voltage (the voltage between input low and
chassis ground1 is 5OOV peak. Exceeding
this value may create a shock hazard.
CAUTION
Connecting PREAMP OUT, COM, or 2V ANALOG
C
XJTPUT to earth while floating input may
damage the instrument.
CAUTION
The maximum voltage between input high
and input low is ZXlV rms. DC to 60Hz sine
wsve (10 seconds maximum in mA ranges).
Exceeding this value may cause damage to
the instrument.
2.7.3 Making Voltage Measurements
The Model 617 can be used to measure voltages in the range
of *lOpV to +2COV. In principle, the instrument operates
much like an ordinary DMM, but its special characteristics
allow it to make measurements in cases where an ordinary
DMM would be unable to perform well. In particular, the
very high input resistance of 2oOTSl (2 X 1OW) allows it to
accurately measure voltage sources with high internal
resistances. In contrast, an ordinary DMh4 may have an in-
put resistance of only loMa. resulting in inaccurate
measurements because of instrument loading.
Use the procedure below to make voltage measurements.
1. Turn on instrument power and allow it to warm up for two
hours to reach rated accuracy.
2. Check to see that the voltage function is selected by press-
ing the VOLTS button. Use the autorange mode, or select
the desired range with the ranging pushbuttons.
3. To achieve specified accuracy, especially on the lower
ranges, it is recommended that you zero the instrument. To
do so, first enable zero check and then press the ZERO
CORRECT button. Correcting zero in the lowest range of
any function will correct all ranges because of internal scal-
ing.
NOTE
The input circuit configuration changes with
zero check enabled. See paragraph 2.11.1.
4. Connect the Model 6011 triaxial input cable or other
similar cable to the rear panel INPUT jack on the instru-
ment. For sources with high output resistance, the cable
should be kept as short as possible to minimize cable
capacitance.
5. If response time and leakage resistance are considerations,
place the instrument in the guarded mode as described in
the next paragraph.
6. Connect the other end of the cable to the voltage to be
measured, as shown in Figure 2-4. Disable zero check.
7. The reading may be obtained directly from the display.
The exponent can be placed either in the alpha or numeric
mode, as described in paragraph 2.5.
2-8
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