Operation - Keithley 171 Instruction Manual

SECTION 2.
OPERATION
b. Shielding.
1. Electric Fields. Shielding is usually neces-
say when the Fnstrument is in the presence of very
large a--c fields or when very sensitive meaS"rementS
are being made. The shields of the measurement
circuit and leads should be connected together to
ground at only one point. This provides a "tree"
configuration, "hid, minimizes graund loops.
3. Other Considerations.
a) Voltmeter Measurements. "se shielded input
leads when source resistances are greater than 1
Kilohm or when lang input cables are used.
b) current Measurements. on the IlLA and p.4
current ranges, no special shielding precautions
need be taken. However, on the I microampere
range, shielded input leads are recommended.
c) Resiseance Measurements.
Shielding of input
leads and source are recommended for measurements
on the 10 megohm through 1000 megotm ranges to
prevent erroneous readings.
C. Floating. The circuit ground to chassis ground
isolation is greater than 100 megohms shunted by less
than 0.02 microfarad. Circuit ground may be floated
up to 2500 volts With respect to chassis ground in a11
modes. TO use the Model II1 for floating measurements,
disconnect the shorting link between the LO and CASE
terminals on the front panel.
d. Source Impedance. The Model 171 has an input
resietance of 10% on the 10 Ill" to 1-v ranges. The
loading error *or these ranges Will be less than 0.003%
(negligible with respect to full scale readings) when
the source resistance is 30 kilahm or less. On the
10 v to 1000 " ranges, input impedance is greater than
10's?. Loading error will be negligible when the source
resistance is less Lhan 300 duns.
2-2. CONNECTIONS. (refer to Figures 2 and 3)
a.
Input. Three binding posts are provided on the
front panel for input connections. The terminals are
color coded as follows: red = input high, black =
input low, and green = chassis ground. The shorting
link should be connected between LO and CASE for
grounded operation. The link should be removed for
floating operation.