Fieldbus Function Block Stays in OOS Mode Primary Software: Driver Software>>NI-FBUSPrimary Software Version: 2.3.5 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: My function blocks won't transition into Auto mode. I have checked that the resource block is in Auto mode. Why won't my other blocks go into Auto mode? Solution: One of the more confusing aspects of Fieldbus for the novice user is the function block modes -- what the modes are and how to get a block into the desired mode. The most common modes are Auto, Cascade, Manual, and Out Of Service (OOS). In Auto mode, the block is running under its normal automatic control. In Cascade mode, the block is running under automatic control and is receiving its Set Point from another function block. (The PID and AO often receive their Set Points from a wire connecting an upstream block.) In Out Of Service mode, the block is not running at all. Normally, this mode is used during block configuration. Also, some devices require that the function block be in Out Of Service mode when writing certain parameters. In Manual mode, you can write the output of the block directly, so the block is under manual rather than automatic control. The MODE_BLK parameter for a function block has four fields - TARGET, ACTUAL, PERMITTED, and NORMAL. PERMITTED and NORMAL are defined by the device manufacturer. PERMITTED contains a list of all allowable modes for that block. NORMAL is the mode the device manufacturer expects the block to be in during normal use. The ACTUAL mode is the operating mode of the function block on the device. TARGET is a field that is writable by the user. Writing this field tells the device to change to the specified mode. The device will attempt to change the mode. If it is successful, the ACTUAL mode will reflect the target mode. The Fieldbus device must be configured to execute the block before the block can go into Auto mode. If the block is not currently scheduled for execution, it will always be in Out Of Service (OOS) mode. This is the primary cause for blocks not transitioning to Auto mode on demand. A block is scheduled by placing it in a Function Block Application (FBAP) window and downloading the project to the device. Before this is done, the function block is not actually executing on the device - it is Out Of Service. Any writes to change its mode are ineffective until the block is scheduled to execute on the device. If the device still cannot change its mode to the target, you can diagnose the problem by looking at the following: 1. Make sure that the resource block is in Auto mode - not OOS. Double-click on the resource block. Look at the mode buttons. Click on the Auto button if it is not already depressed. 2. If the resource block will not go into Auto mode, check its BLOCK_ERR parameter and fix whatever is causing the error. 3. Double-click on the desired I/O function block. Look at the mode buttons. Click on the Auto button if it is not already depressed. Wait a few seconds to see if the MODE_BLK.ACTUAL transitions to Auto. 4. If the I/O function block will not go into Auto mode, check its BLOCK_ERR parameter and fix whatever is causing the error. If the device is an FP-3000, you can also look at the additional parameters on the Diagnostics tab in the function block’s parameter window. Note that the LAST_BLOCK_EVENT is not cleared after an error condition clears. Check the time stamp to determine whether the event you are looking at is current. Related Links: Attachments:
Report Date: 05/13/1999 Last Updated: 06/23/2004 Document ID: 1LC9AEQT |
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