Hi,
I am trying to output DAC voltage signals from a LI-7550 control box for a LI-7200 to monitor flow rate, motor drive remotely. The LI-7200 manual is a bit cryptic on how to connect these DAC cables to a datalogger. It appears they output a 0-5V signal. Is the best way to interface this is using RS-232 (C channels on the CR1000) or in differential ports using something like the VoltDiff command.
Does anyone have any experience logging this sort of data from the LI-7550 control boxes? Our other data is coming in to our logger via SDM but these variables can only be output via DAC or ethernet.
Here's what the LI-7200 manual says:
"For example, to configure DAC #1 to output a voltage signal proportional to CO2 mmol/m3, 20 mmol/m3 full scale, select CO2 mmol/m3 under DAC1 'Source', and set 0V = 0, and 5V = 20.
0V 0 (Xo, zero volts corresponds to 0 mmol/m3)
5V 20 (XF, full scale corresponds to 20 mmol/m3)
When a voltage range R is selected, the DAC output voltage V resulting from
a CO2 molar value X is given by
V = R
X Xo
XF Xo
where R = 5V.
The DACs are linear, so in the example above, a measured voltage signal of 3 volts would correspond to a CO2 mmol/m3 value of 12."
Peter,
I assume you could do either. The voltage would be the easiest because you could just use the Volt Diff instruction. You would have to match the wiring to the LI-7550 pinout for the DACs to go to the datalogger and make sure you do the scaling properly in the logger to get from voltages to engineering units. I am sure that LI-COR could help you out at least with the proper wiring. It looks like you could also do RS232 output but that will take some more advanced programming to read the data in serially and parse the string out properly. Since CSI is focused on selling and supporting its own line of gas analyzers, we don't currently have this code in our library. If you would like custom programming let me know offline and I could provide you with a quote and timeline.
Thanks for the reply Ben. I think I may try the simpler of the two and go with trying the VoltDiff command and match the LI-7550 pinouts from DAC to differential ports. I will let you know if we need any custom programming but these are non-essential measurements for us - but we would like them for diagnostic monitoring to prevent bad data from our sensors.