Changing The Default Failsafe Direction; De And Analog Differences; Procedure To Establish Failsafe Operation - Honeywell stt850 SMARTLINE User Manual

1.19.

Changing the Default Failsafe Direction

For HART or DE the 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.

4.1.10 DE and Analog Differences

Failsafe operation is somewhat different between DE and analog operation:

Analog operation – Upscale failsafe drives the Transmitter output to 21.8 mA. Downscale
failsafe drives the Transmitter output to 3.6 mA.

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.

4.1.11 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
Note: The Fieldbus variant has simulation and write protect jumpers in the same location and their
positions are described in
Protect Jumper on Foundation Fieldbus (FF)
Page 44
Figure 15 for the locations of the failsafe and write protect jumpers.
Table 14Error! Reference source not found.. See Section 4.1.12, Write
STT850 Temperature Transmitter User's Manual
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