Acquiring Digital Stream of Data

[Lacksagoo]

Hello,

I've been trying (without great success) to acquire digital data from a lab sensor.  From the manufacturer's guide:

"When excitation voltage is applied, the Decagon CTD sensor makes a measurement.  Within about 140 ms of excitation three measurement values are transmitted to the data logger as a serial stream of ASCII characters.  The serial out is 1200 baud asynchronous with 8 data bits, no parity, and one stop bit.  The voltage levels are 0-3.6V and the logic levels are TTL (active low).  The power must be removed and reapplied for a new set of values to be transmitted.  The ASCII stream contains three numbers separated by spaces.  The first number is water depth in mm, the second number is temperature in degrees Celcius with a resolution of 0.1 degree C, and the third number is electrical conductivity in dS/m, with a resolution of 1 dS/m.  A carriage return follows the three numbers, then the character 't', indicating that this is a CTD sensor, then a checksum character, and finally a carriage return and line feed."

My attached VI is a bit iffy- it probably looks like something that someone used to analog signals might create.  Nevertheless, I was hoping that it would be enough of a starting point for a wiser LabVIEWer to work with.

Thank you very much,

Lacksagoo

[Dennis_Knutson]

That makes no sense.With a serial connection, you do NOT use digital I/O hardware. None of that code is correct. You use a com port on the pc and the LabVIEW VISA functions. There are a couple of serial examples that ship with LabVIEW. Start there and with a terminal emulation program such as Hyperterminal or the VISA test panels in MAX.

[Lacksagoo]

Ah, that's the strange bit.  The cable connected to the sensor came with a 'pigtail' configuration- tinned wires corresponding to signal out, signal ground, excitation, and power ground.  Indeed, the guide said that the sensor should be connected to a data logger (we use the NI-6363).  That's why I'm at a bit of a loss here.

[Dennis_Knutson · Accepted solution]

Does the guide actually say that an NI DAQ card is the same thing as a datalogger. I've never associated the two as being the same. What I think of a datalogger is a stand-alone instrument.

Looking a more details in your original post, the voltage levels are not standard. You may need a level shifter or need to find a USB-RS232 adapter for TTL levels.

[Lacksagoo]

Thank you, Dennis.  I'll look into that.