2.4Changing Default Failsafe Direction
Background
Analog and DE mode differences
ATTENTION
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 printed wiring assembly (PWA).
If your transmitter is operating in the analog mode, an upscale failsafe action will drive the transmitter’s output to greater than 21 mA or a downscale action will drive its output to less than 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. The STDC card initiates the failsafe mode configured through the transmitter when either signal is generated.
The failsafe direction display that you can access through the SFC 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 4 outlines the steps for cutting the failsafe jumper |
| on the transmitter’s PWA. Figure 2 shows the location of the failsafe |
| jumper on the PWA for Release 300 transmitters. |
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.
Continued on next page
2/05 | ST 3000 Release 300 Installation Guide | 13 |