User manual

2-8 Connections Model 6485 and 6487 User’s Manual
Figure 2-8
Basic Model 6487 ohms connections
Noise and safety shields
Figure 2-9 shows typical measurement shielding. In (A), a noise shield is used to prevent
unwanted signals from being induced on the picoammeter input. Amps measurements
below 1A may benefit from effective shielding. Typically, the noise shield is connected
to picoammeter input LO. Additionally, Figure 2-9(B) shows an added safety shield con-
nected to earth ground and Model 6487 chassis. This type of shielding should be used
whenever hazardous voltages will be present in the test circuit.
t^okfkd The maximum safe voltage between picoammeter LO and chassis
ground (common mode voltage) is 505V peak. The Model 6487 does not
internally limit the LO-to-chassis voltage. Exceeding 505V can create a
shock hazard.
If it is possible for the DUT or external supply to present more than 505V
to the input HI, it is imperative that the connection between input LO and
the external voltage source be sufficiently low impedance and capable of
carrying the short-circuit current of the source, in order that the LO not
exceed 505V.
`^rqflk The LO to chassis breakdown voltage is 505V. Exceeding this voltage may
cause damage to the instrument.
HI
LO
DUT
INPUT*
LO
HI
V-SOURCE OUTPUT
6487
* Maximum Continuous Input: 505V Peak