Current Measurements - Keithley 486 Instruction Manual

SECTION 3
Front Panel Operation
input, the display will read -4.39998mA. Thus, the dy-
namic
measurement range
of the Model 486 is OmA to
439998mA, which is still 439,998 counts.
Rel is enabled by pressing the REL key CREL indicator
hmw on). Pressing REL a second time disables the fea-
ture. The REL indicator (on or offl denotes the REL state
of the displayed
measurement hrrent or
V/I ohms).
Perform the following steps to establish a relative
baseline:
1. Disable rel, if presently enabled, by pressing REL.
The REL indicator wilI turn off.
2. Selectacorrentrange orV/Iohmsrsnge(Mode1487)
that is appropriate for the anticipated
measurement.
3. Connect the desired baseline level to the
input
of the
Model 486 /487. Model 486 /487.
4. 4. Press the REL key. The display will zero and the REL Press the REL key. The display will zero and the REL
indicator will turn on. The previously displayed indicator will turn on. The previously displayed
reading will be the stored level. reading will be the stored level.
NOTES:
.l. Enabling zero check with a rel baseline established
will remove the applied signal from the input with a
displayed reading as follows:
Displayed reading = input signal-relative baseline
= 0 -relative baseline
= -relative baseline
2. Disabling rel cancels the rel baseline value on that se-
lected function. A baseline established on the other
function is not affected.
3. To store a new baseline, rel must first be disabled and
then enabled again. the new value will be stored
with the first triggered conversion.
4. Setting the range lower than the suppressed value
will overrange the display.
5. Enabling Rel while displaying dashes or an over-
ranged condition will cause the RJZL indicator to
blink until a valid on-scale reading becomes avail-
able. At that time, the REL indicator stops blinking
(stays on) and the valid on-scale reading is used as
the Rel baseline value.
3.5.6
Current Measurements
Input Connector
Terminal identification for the Model 486/487 input con-
nector is shown in Figure 3-3. It is a 3-lug female tiax
connector that will mate to a cable terminated with a
3slot male triax connector. The center conductor of the
connector is connected to input high, the inner shell is
connected to input low, and the outer shell is connected
to chassis ground.
CAUTION CAUTION
To prevent damage to the Model 486/487, do To prevent damage to the Model 486/487, do
not exceed the maximum input levels speci- not exceed the maximum input levels speci-
fied in Figure 3-3. fied in Figure 3-3.
Max Overload
2nA - 2W Range; 35OVdc
2OpA - Zm.4 Range: 50 "dc
Trim Input Connector (3.Lug)
Current source connections to the Model 486/487 are
shown in Figure 3-4 using the supplied triax-to-alligator
cable. Note that if the current source is equipped with
3-lug triax female connector, a 3-slat t&.x-to-t&x cable
(Model 707%TRX) could be used. A shield (connected to
circuit low) should be used to minimize noise when mak-
ing measurements below l@.
WARNING
A shock hazard, that could cause severe in-
jury or death, exists when the input signal is
at 424V peak or more. When this voltage
level is present, a safety shield
must
be used
as shown in Figure 3-4. Chassis ground of
the Model 486/487 must be connected to the
safety shield. Also, a grounding wire (18
AWG or larger) must be attached securely to
the safety shield at a screw terminal de-
signed for safety grounding. The other end
ofthegroundwiremustthenbeattachedtoa
known safety earth ground.
3-a