PFI causing voltage error?

[Butch Husky]

I'm using an E-series to gather some signals, and because I need pretrigger
scanning, I have to trigger off a Programmable Function Input. Fine and
dandy,
EXCEPT that whenever I hook up the PFI, it offsets my voltage signal By like,
5 volts! Specifically, this occurs when I hook in AISENSE from the low end
of my
signal up to the AISENSE pin (The acquisition must be NRSE because of the
signal conditioner I have). What could possibly cause this?
I've checked my grounding a million times, there's nothing floating at all.
Is there some kind of configuration (beyond hooking up a signal and typing
in "PFI 0" to the
Analog Start.vi) that I need to do before I can use PFI0 as a trigger input?

[markwysong]

Butch,

I'm wondering why you need to use a PFI. AI start lets you select an
analog input channel as a trigger, if you are scanning the signal from
which you wish to trigger. I believe that PFI0 is used when you wish to
trigger from a signal which is not being scanned.

I'll admit, while I'm not sure why when you make this connection, you're
getting the offset, but in looking at the E-series connections, I've
noticed that in NRSE mode, the PGIA which is reading your input is
floating and not referenced to the board ground. PFI0, however, is
referenced to a digital ground, and thus your offset, because the NRSE
(-) (AISENSE) and digital ground are NOT referenced to one another.

I would try using your input channel as the trigger channel instead of
PFI0.
Give that a shot.

Mark

In article <397f50dc@newsgroups.ni.com>,
"Butch Husky" wrote:
>
> I'm using an E-series to gather some signals, and because I need
pretrigger
> scanning, I have to trigger off a Programmable Function Input. Fine
and
> dandy,
> EXCEPT that whenever I hook up the PFI, it offsets my voltage signal
By like,
> 5 volts! Specifically, this occurs when I hook in AISENSE from the
low end
> of my
> signal up to the AISENSE pin (The acquisition must be NRSE because of
the
> signal conditioner I have). What could possibly cause this?
> I've checked my grounding a million times, there's nothing floating at
all.
> Is there some kind of configuration (beyond hooking up a signal and
typing
> in "PFI 0" to the
> Analog Start.vi) that I need to do before I can use PFI0 as a trigger
input?
>
>


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[Butch Husky]

Well, I would do that first, but apparently, I can't trigger off the channel
I scan from if
I have multiple channels and require more than one pretrigger scan. Or so
the manual says. And I tried it, of course getting an error. I'm not
sure WHY that is, but such is the board's limitation.

[markwysong@my-deja.com]

Okay, I've read a little more on it, and I see your limitation as you
stated. If you must use PFI0, you could first make sure that it is not
connected as an output. First, before your AI config, call the
AI->Misc->Route Signal VI, and route PFI0 to "none". This will make
PFI0 an input.

Next, you could try connecting the digital ground and the input signal
(-) together.



In article <39805c05@newsgroups.ni.com>,
"Butch Husky" wrote:
>
> Well, I would do that first, but apparently, I can't trigger off the
channel
> I scan from if
> I have multiple channels and require more than one pretrigger scan.
Or so
> the manual says. And I tried it, of course getting an error. I'm
not
> sure WHY that is, but such is the boa
rd's limitation.
>


Sent via Deja.com http://www.deja.com/
Before you buy.