Switching of analog measurment signals

Question

Hello,
in our LabView applications we have to measure several voltages and
currents. We use a AT MIO 16 E 10 DAQ card, but it is not good enough
for 2 voltages 2 currents. Therefore, we use exernal GPIB measuring
instruments for them (Keithley 2000 a.a.).
However, I think we could come along with only one Keithley 2000 since
the timing is no issue (1 scan per sec is enough). I need some switch
controlled by LabView that switches the analog measuring signals to
two Keithley 2000 (analog) inputs (one for voltage, the other for
current measurement, respectively).
I found out that I can't do this with the DAQ card alone. I can't use
the analog outputs since I don't want a A/D - D/A conversion included.
Note that the measuring volta
ges can be ~100 mV.
But I could be wrong since I am actually a software guy so please
correct me if this is possible with the DAQ card only.
My idea is as follows:
I could use the digital outputs of the DAQ card and connect them to
some opto coupler or relais with TTL input. The opto couplers or
relais would switch the analog measuring signals according to the
digital outputs of the DAQ card and finally according to LabView.
I couldn't find such a switcher board in the NI catalog. They have
switchers, but they seem to switch voltages >3V only. But maybe
someone suggests a board from another company which suits better.
I just wouldn't like so much soldering my own board since my knowlege
of opto couplers, relais and hardware in general is really limited.
Best regards
Johannes

Answer 1

Hi Marcus,
thanks for your answer.
I was probably not clear about what I want. The solutions you suggest
seem to be far to complex. As Nirmal pointed out, I actually only need
high quality optocouplers, no more.
On Thu, 25 Mar 2004 09:30:26 -0600 (CST), Marcus G wrote:
>Hello Johannes,
>It sounds like you're setting up a system that requires four analog
>inputs (two voltage and two current), and you would like to use an
>analog trigger to switch between which signals are measured.
No. I just want to use the digital outputs of the DAQ card to switch
optocouplers. The optocouplers will switch between several analog
measuring signals. They should route these signals to one analog input
of a Keithley 2000.
>There are
>several options of
how you can set up such a system.
>In terms of measuring the four analog inputs, you should be able to do
>this with a DAQ card alone. Many of our cards, including the
>AT-MIO-16E-10 (also called a 6020E), have 16 analog input channels
>that have an input range of +/-10V.
I don't want to measure the four analog inputs with the DAQ card since
it isn't precise enough. The input range is too high for some of the
analog inputs and the resolution is too low. Also, I can't modify the
input range of the DAQ card at runtime. Therfore, we are using
external instruments (Keithley 2000 a.a.) for the measurements. My
idea was to only use one instrument for the four analog input signals.
Then I must provide the switching between the four analog inputs. The
idea was to control (switch) some optocouplers with the digital
outputs of the DAQ card. The optocouplers should route one of the four
analog signals to one Keithley 2000. I set the digital outputs of the
DAQ card in the LabView program. Also, t
he LabView program configures
the Keithley 2000 and reads the measuring values from the GPIB. That's
all.
Regards
Johannes