wiring anemometer to NI 9219 or similar

[Duke_Nuke]

Hello,

I'm trying to wire a Davis Instruments 7911 anemometer to a module on my cDAQ, specfically the NI 9219.

Based on the manufacturer's wiring diagram for the anemometer there are 4 leads:

• a yellow lead that is direction excitation
• a red lead that acts as the common/ground
• a green lead that is the wiper for the potentiometer
• a black lead which is connected to a reed switch for wind speed data

I'm trying to wire this into the NI 9219, but I'm unsure if it will provide sufficient excitation for the anemometer. I believe the anemometer requires 5 volts based on the connector it came with.

Does anyone have experience with this?Boards that they could suggest if this one doesn't work? It's a simple cup and vane anemometer.

[Kelle]

Duke, the 9219 shouldn't be used as a voltage source.  From the module's page, it is purely an input module.  It sounds like you get the wind direction using the POT's resistance.  The 9219 can do that by sourcing a current and then measuring the resistance from the resulting voltage.  You can find the wiring in the manual.  Looks like yellow at 3 and green at 5 for 2 wire resistance measurement.  For your wind speed, it looks like it is counting pulses, so probably an AI task, with red at lo/5 and black at high/4.  I could have that backwards, but then you will still get pulses, just flipped of what it was in the other config.

[Henrik_Volkers]

You should be able to use the 9219 to read the open contact and to read the pot.

On page 9 in the manual / spec     you can find the connection table:

So my suggestion:

For windspeed (open contact) configure CH0 as digital open contact input (only supported in cRIO systems as stated in the manual):

Red (gnd) to CH0-pin5

Black( speed contact) to CH0-pin3

if open contact mode is not possible add 10kOhm resistor between the two pins and measure the resistance (10k or 0 Ohm 😉 )

For Direction  configure CH1 for 2 wire resistance:

Red (gnd) to CH1-pin5  (both channels share the same gnd wire)

Green (pot wiper) to CH1-pin3

Max sample speed is 10ms  so max frequency to detect is 50Hz . IF the pulselength of the speed sensor is to short or the speed signal has a higher frequency you migth think of building a simple frequency to voltage converter.....(say each rising slope of the pulse trigger a pulse of length t_p  ms followed by a low pass filter...)

[Duke_Nuke]

Hi Guys,

Thanks for you  input, I've been scratching my head trying to figure this out.

Henrik: So for the CompactDAQ I can't configure CH0 as a digital open contact correct? I have the NI 9135. Also, I will have to split the two circuits between two channels? or can I follow Kelle's suggestion all on one channel? Thanks for your help!

[Duke_Nuke]

Kelle,

Thank you for your input, much appreciated! I need to read these measurements simulatneously during operation. I'm unsure how to ground this system. I understand you need to read the voltage drop across the POT but don't you still need the red in CH0-pin5? Or should I connect red to the Chassis ground and proceed as you've suggested?

Thanks,

[Kelle]

Duke, I think you should be able to just create 2 tasks in LabVIEW to have these two measurements read in simultaneously.  When you are reading the resistance of the POT, it only requires the yellow and green wire.  I think it would be good to go and only connect the yellow and green wire and see how your readings are coming out in relation to the direction of the wind vane.  I do not believe you need the ground (red wire) in order to read your wind direction since it is purely a resistance measurement and you already have 2 wires for that (yellow and green).  You will need the red wire for the wind speed though, and I believe the wiring should be as suggested above.  I do not have access to this anemometer, so I would suggest you try out the wind direction wiring first, and then once you get that working, try out the wind speed.  That will probably be the best way to proceed.

[Henrik_Volkers]

Had a closer look 😉

Seems that the contact and the pot share one common ground. 

and the pot value is 20k Ohm and the max range for the 9219 is 10k (10.5k)

You want to use one channel only, so I propose to test the following:

Use one channel 4 wire resistance (fast mode):

Additional you need a 5 10kOhm resistors

The values read should now be a linear 0 to 5k scale for the direction (2.5k south) plus 5k of the switch

There is still one undefined position, if the wiper is at ground, but you can change the 10k parallel to the pot to a lower value (8,5k)   or add 200 Ohm to the lower 5k (build from two 10k)