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Installation - 3
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Table 3-3. 4-Pin Connector Configurations
PIN TRIGGER FAULT/INHIBIT DIGITAL I/O
1 Not used FLT Output Output 0
2 Not used FLT Common Output 1
3 Trigger Input INH Input Input/Output 2
4 Trigger Common INH Common Common
When functioning in Fault/Inhibit mode, the fault (FLT) output, also referred to as the DFI (discrete fault
indicator) signal, is an open collector circuit that pulls the positive output low with respect to the negative
(chassis-referenced) common. The high impedance inhibit (INH) input, also referred to as the RI (remote
inhibit) signal, is used to shut down the dc source output whenever the INH + is pulled low with respect to
the INH (chassis-referenced) common. Figure 3-9 shows how you can connect the FLT/INH and trigger
input circuits of the dc source.
In example A, the INH input connects to a switch that shorts the Inhibit pin (+) to common whenever it
is necessary to disable output of the unit. This activates the remote inhibit (RI) circuit, which turns off the
dc output. The front panel Prot annunciator comes on and the RI bit is set in the Questionable Status
Event register. To re-enable the unit, first open the connection between pins INH + and common and then
clear the protection circuit. This can be done either from the front panel or over the GPIB.
In example B, the FLT output of one unit is connected to the INH input of another unit. A fault condition
in one of the units will disable all of them without intervention either by the controller or external circuitry.
The computer can be notified of the fault via a service request (SRQ) generated by the Questionable
Status summary bit. Note that the FLT output can also be used to drive an external relay circuit or signal
other devices whenever a user-definable fault occurs.
FLT
Output
INH
Input
B) FLT Example with Multiple Units
FLT
Output
INH
Input
Switch
(Normally
Open)
INH Common
INH Input
A) INH Example with One Unit
INH FLT
. . . .
INH FLT
. . . .
NOTE: Connectors
are removable
+ - +
+ - +
4 3 2 1
4 3 2 1
4 3 2 1
C) Measurement trigger example
TRG N.U.
. . . .
+
4 3 2 1
NOTE: Connectors
are removable
Trigger signal
or contact closure
Signal Common
Figure 3-9. FLT/INH Examples
In example C, when functioning as a measurement trigger input, a negative-going edge signal applied to
the TRG input sends an external trigger signal to the trigger system. You can either apply a negative-
going edge signal to the TRG input pin (referenced to common), or apply a contact switch to short the
TRG input to common. Note that in this configuration, pins 1 and 2 are not used.