data acquisition with hbm mgc

[rlauri]

I am using LabView together with the MGC amplifier from HBM. I downloaded the LabView driver for this instrument from NI homepage. Now I have a problem with data acquisition.
When I start measuring, the data displayed on the graph seems unstable. (This only happens with binary output, in Ascii the graph is stable and fine (but too slow).)
Perhaps it is a communication problem between PC and device.
Serial communication:
Baudrate. 9600
Databit: 8
stopbit: 1
parity: even
software handshake: X-on, X-off

Can anybody help me.

[JRA]

What exactly do you mean by it being unstable? If the ASCII works fine (just slow) then we know that your connection to the device is working properly. Any problems would either be coming from the driver or the hardware itself. Let us know exactly what is happening and maybe we can help you out.

[rlauri]

With 4 byte binary output, 3 bytes are measurments and 1 byte is status. It can work fine in a few seconds,
and then suddenly the value of the measurments are about ten times bigger then the measurments a few seconds earlier.
The status byte comes out with every possible status and shifting rapidly.
After about 5-20 seconds (sometimes longer) the values return to the correct ones.
What can be the problem? Is it possible that a byte was lost in the process? How can I fix this?

[JRA]

My guess is that the instrument is sending back bad data. It sounds as though you are reading the data back the same way for an extended amount of time and you only get this "bad data" a few seconds out of that time. I have run upon more than a few instruments which are not very complaisant, and this could be a similar issue. Try finding another program to interface with the instrument and see if it exhibits the same behavior. This will tell you whether the instrument is causing the problem or the VI.

[rlauri]

I found out that some bytes were missing, and thought
that the flow-control commands were mistaken for data.
I turned of software flow control (X-on, X-off) and
now everything works fine. Is it possible to
communicate with the instrument without using flow control?