Rockwell-automation T80004 Application Note Field Loop Configuration Instrukcja Użytkownika Pobierz pdf (Strona 38)

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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_CPRM_B

ENABLE_C ENABLE_A ENABLE_B

LOAD

LOAD_A

LOAD_B

LOAD_C

LOAD

= I

LOAD_A

+ I

LOAD_B

+ I

LOAD_C

FIELD_RTN

SENSE_A

SENSE_C

SENSE_B

LOAD

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 ... 55 56

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