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1/99 SMV 3000 Transmitter User’s Manual 95
8.3 Changing Default Failsafe Direction
Background
Transmitters are shipped with a default failsafe direction of upscale. This
means that the transmitter’s output will be driven upscale (maximum
output) when the transmitter detects a critical status.
You can change the direction from upscale to downscale (minimum
output) by cutting jumper W1 on the main printed circuit board (PWA) of
the electronics module.
Analog and DE Mode
Differences
If your transmitter is operating in the analog mode, an upscale failsafe
action will drive the transmitter’s output to 21.8 mA or a downscale action
will drive its output to 3.8 mA.
If your transmitter is operating in the DE mode, an upscale failsafe action
will cause the transmitter to generate a “+ infinity” digital signal, or a
downscale failsafe action will cause it to generate a “– infinity” digital
signal. The STIMV IOP module interprets either signal as “not a number”
and initiates its own configured failsafe action for the control system.
ATTENTION
The failsafe direction display that you can access through the SCT only
shows the state of the failsafe jumper in the transmitter as it correlates to
analog transmitter operation. The failsafe action of the digital control
system may be configured to operate differently than indicated by the state
of the jumper in the transmitter.
Procedure
The procedure in Table 26 outlines the steps for cutting the failsafe jumper
on the transmitter’s PWA. Figure 27 shows the location of the failsafe
jumper on the main PWA of the electronics module.
The nature of the integrated circuitry used in the transmitter’s PWA makes
it susceptible to damage by stray static discharges when it is removed from
the transmitter. Follow these tips to minimize chances of static electricity
damage when handling the PWA.
• Never touch terminals, connectors, component leads, or circuits when
handling the PWA.
• When removing or installing the PWA, hold it by its edges or bracket
section only. If you must touch the PWA circuits, be sure you are
grounded by staying in contact with a grounded surface or wearing a
grounded wrist strap.
• As soon as the PWA is removed from the transmitter, put it in an
electrically conductive bag or wrap it in aluminum foil to protect it.
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