Changing The Default Failsafe Direction; De And Analog Differences; Procedure To Establish Failsafe Operation - Honeywell ST 700 User Manual

5.6

Changing the Default Failsafe Direction

Transmitters are shipped with a default failsafe direction of upscale. This means that the Transmitter
output will set the current output to upscale failsafe (maximum output) upon detection of a critical
status. You can change the direction from upscale failsafe to downscale failsafe (minimum output) by
moving the top jumper located in the Electronics module.

5.6.1 DE and Analog Differences

Failsafe operation is different between DE and analog operation:

Analog operation – Upscale failsafe drives the Transmitter output to 21.8mA. Downscale
failsafe drives the Transmitter output to 3.8mA.

DE operation – Upscale failsafe causes the Transmitter to generate a + infinity digital
signal. Downscale failsafe causes the Transmitter to generate a – infinity digital signal.
The Transmitter electronics module interprets either signal as not-a-number and initiates its own
configured failsafe action for the control system.

5.6.2 Procedure to Establish Failsafe Operation

The failsafe direction display accessible via the Toolkit shows only the state of the
jumper as it correlates to analog Transmitter operation. Failsafe action for the DE control
system may be configured to operate in a manner different from analog, as indicated by the
state of the Transmitter jumper.
The integrated circuits in the Transmitter PWA are vunerable to damage by stray static
discharges when removed from the Electronics Housing. Minimize the possibility of static
discharge damage when handling the PWA as follows:
Do not touch terminals, connectors, component leads, or circuits when handling the PWA.
When removing or installing the PWA, handle it by its edges or bracket section only. If you
need to touch the PWA circuits, be sure you are grounded by staying in contact with a
grounded surface or by wearing a grounded wrist strap.
When the PWA is removed from the Transmitter, put it in an electrically conductive bag, or
wrap it in aluminum foil to protect it.
The following procedure outlines the steps for positioning the write protect and failsafe jumpers on
the electronics module. See
Revision 8.0
Figure 19 for the locations of the failsafe and write protect jumpers.
ST 700 SmartLine Pressure Transmitters User's Manual
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