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Message ID: 1138     Entry time: Thu Nov 4 22:18:31 2010
Author: Alastair 
Type: Computing 
Category: Computing 
Subject: Changes to model 

I've been working on getting the model to switch the boost on and off based on the transmission pd signal.  So far I have the software part working but not the hardware.

In terms of software, initially I tried modifying the epics atf1.db file.  I added  a calc channel that compared the trans_pd value to a user input channel from the MEDM screen.  I could get this to switch, but got stuck at the point where I tried to write this back out through the DAC.  While you can use an 'ao' channel in epics to do this, we want instead to write out through the front end.  I set up an epics channel that could write out through the front end, by putting it into the model but got stuck trying to work out how to write the calc channel to the channel that is connected to the DAC.  Making them the same channel didn't work and I couldn't find a way to transfer a value from a calc channel to an 'ai' channel.

Instead I got it to work by putting doing the comparison in the Simulink model.  The trans_pd epics value is compared to a user input MEDM value, and the binary output of this then toggles a switch that sets DAC output 10 high or low.  One nice thing about this is that it doesn't require any manual editing of the .db file.

There is one problem with connecting this up right now.  Frank thinks the DAC output is probably differential (we measure 5v out on the boost controller channel when connected to a scope, but 10v on a multimeter), and if we connect it to a grounded piece of equipment (such as the boost input on the PDH box) we will be shorting the output.  We should take the DAC card out of the rack and check that this is the case.  If so then it seems we need a differential input on the boost switch and everything else that we are controlling from the DAC (such as the slow input on the laser).

 

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