24VDC Input NI USB 6009

[davetrombon]

Hello!

I'm developing a program in LabView in which I need to run some code everytime a +24VDC signal received from a digital sensor is detected. I was planning to use my NI USB 6009 but, as far as I know, the analog input is limited to +-20V in differencial mode (10V max in each pin). I was looking in the datasheet and I saw that the DAQ has a +-35V overvoltage protection, and then I thought: As far as I only need to start my code when the signal comes, would be possible to connect my +24VDC to the analog input of my DAQ withouth damage it?

Thank you!

[Henrik_Volkers · Accepted solution]

You can use a voltage divider (one resistors of about 20k from sensor to AI and 10k from AI to AGND, if your sensor output can handle that load)  , or in the most simple way a 100k resitor (than will limit the input current) and a 4.7V (for digital input) or 9.6V Z-Diode (for AI) to limit the input voltage. 

More protection would be a optocoupler , the 24V with a 10k resistor drive the LED and the output of the coupler has 10k (or 4.7k) to 5V(6009) pullup.

[johnsold]

Why take a chance? For 0.05% of the cost of a USB-6009 you could add a series resistor and diode clamp to a voltage within the operating range of the device.

I always consider overvoltage protection to be something which is there to prevent damage from accidental overvoltages, not something which will be used routinely hundreds or thousands of times as part of normal operation.

Also, consider that they do not specify how much current the device will draw under overvoltage conditions or what the measured value will actually be. Some op amps for example will reverse the polarity of their outputs under overvoltage conditions. What if one of those is used internally in the USB-6009 and the converted value goes negative?

Lynn

[davetrombon]

Thank you very much for the answers 🙂

[Vishnuprashanth]

Hello,

I am trying to connect NI USB 6009 to M12 cable but I don't know which wire has to be connected to which port. I have 7 sensors from which I need an input. Kindly guide me how to make the connections.

Thank you,

Vishnu.

[Dennis_Knutson]

What's an M12 cable? What sensors are you talking about? Why hijack an old and probably unrelated thread?

[Vishnuprashanth]

I didn't know how to post a new one. I'm using M12 4 pin cables for Pressure switches(http://www.hydac.com/de-en/products/sensors/pressure-sensors/electronic-pressure-switches/eds-3100.h... and Progressive distributor valves( http://www.skf.com/group/products/lubrication-solutions/lubrication-system-components/lubricant-dist... ).

Thank you.

[Vishnuprashanth]

M12 4 wire cable(http://www.ifm.com/products/my/ds/EVC005.html)

[Dennis_Knutson]

I'm not going to do all of your basic research for you. The pressure sensors have an analog output. Presumably, one of the m12 wires is this and another is ground. These need to be connected to ai0;6 and ground of the 6009

[Vishnuprashanth]

Thanks for the information.