Rockwell Automation T80004 Application Note Field Loop Configuration - Manual (Page 38)

Trusted
TM
AN-T80004 Field Loop Configuration
Issue 10 Jun 13 AN-T80004 38
Analogue Outputs
The Trusted T8480 Analogue Output module may be considered as a current controlled digital output
module and it has similar termination and characteristics. The specific differences are listed in this
section.
Module circuit
Like digital output modules, the T8480 has channels arranged in power groups, each supplied by a
common failsafe switch.
Instead of six FET switches, the T8480 has three current controlling switches and three shutdown
switches. The demand current is divided between the three slices which interact and ensure that the
total loop current remains as constant as possible during module faults and hot-swap pairings.
Line Monitoring
There is no no-load threshold for analogue outputs.
The states reported by an analogue output are similar to digital outputs, and are summarised below.
No field supply voltage (state 1)
This operates in a similar way to digital outputs. The module cannot guarantee to supply the required
current if it has insufficient supply voltage (for comparison, digital outputs will still switch but the
diagnostics is blind).
Output de-energised (state 2)
This state occurs with a load fitted when the current demand is negative.
Open circuit in field wiring or load (state 3)
This occurs when the load impedance is too high for the channel to drive the required current, but the
supply voltage is acceptable.
TOP_RAIL
PRM_A PRM_C PRM_B
ENABLE_C ENABLE_A ENABLE_B
L
O
A
D
I
LOAD_A
I
LOAD_B
I
LOAD_C
I
LOAD
= I
LOAD_A
+ I
LOAD_B
+ I
LOAD_C
V
FIELD_RTN
R
SENSE_A
R
SENSE_C
R
SENSE_B
V
LOAD