PXI-8431: Serial ports not functioning

[PMende.Wisc]

I recently installed a PXI-8431 RS485/RS422 serial port expansion card in my lab's NI computer (chassis is a PXI-1042Q). After installation, I attempted to make a connection with an RS422 enabled device and failed. I have been able to achieve a connection to this device via the serial port on a PXI-8106 embedded controller, but each of the 4 serial ports on the PXI-8431 has failed to achieve recognition of the device. Each port is recognized by HyperTerminal.

The connection runs over 500ft of cable. Pin 5 is grounded, and pins 2 and 3 are used for the transfer of commands to, and data from, the sensor. The signal runs at 19200 baud/8 data/no parity/1 stop bit/handshake off. Using these settings I am able to achieve a signal over the embedded controller, but using identical settings yields nothing over any of the ports in the expansion slot.

If anyone has any idea what the problem might be, I'd appreciate any help. 

[Online_Courses]

Hi,

Would you please describe what you mean by an RS422 "enabled" device?

The serial port of the embedded controller is RS232.  

Is your instrument capable of communicating in RS232 and RS422?

The pin configuration that you described is RS232.

Regards,

Sammy Z.

[PMende.Wisc]

As far as I am aware, the device has only RS422 capabilities, and not RS232. However, my knowledge of the two communications standards and the differences between them is very limited. I was under the impression that RS232 was not capable of transferring data over distances of 500ft. I have another device that is RS485, and the wiring diagram that came with it describes a pin configuration that is exactly the same as my RS422 sensor, though I have not wired it yet. What sort of configuration should I be looking for if I want to use RS422 or RS485 communications?

[Sammy Z]

Hi,

Would you please provide the brand and model number of the device?

Thanks,
Sammy Z.

[JasonSmith]

Everything you describe sounds like RS-232, except for the 500 ft distance. An RS-422 connection should have four wires for data--two for Rx and two for Tx. 500 feet is far more than I would expect from RS-232, but it could be working with the exact combination of transmitters and receivers on your instrument and the 8106 controller. The low baud rate could be helping it work.

Assuming that your device is RS-232, you won't be able to communicate with it through your PXI-8431 board.  You could try it with a PXI-8430 RS-232 board, but as you said 500 feet is a much longer distance than would be normally operable with RS-232. Usually the limit is considered to be more like 50 feet, although the actual limit will depend on the cables and devices used.

Are you sure that there isn't some form of RS-232 to RS-422 converter already present on your cable near the connection to the 8106 controller? If there is already a converter such as this present, then you would need to remove it from the line in order to communicate through the PXI-8431 board.

-Jason

[PMende.Wisc]

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Sammy Z wrote:

Hi,

Would you please provide the brand and model number of the device?

Thanks,
Sammy Z.

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You may find the product data sheet here: http://www.gillsensors.co.uk/content/datasheets/Motorsport/R-Series_Sensor.pdf 

[Sammy Z]

Hi,

Is there a more detailed manual that you have access to?

Where were you able to see the pinout? (5 for Gnd, 2&3 for communication)

Regards,

Sammy Z.

[PMende.Wisc]

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JasonS wrote:

Are you sure that there isn't some form of RS-232 to RS-422 converter already present on your cable near the connection to the 8106 controller? If there is already a converter such as this present, then you would need to remove it from the line in order to communicate through the PXI-8431 board.

-Jason

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I simply have two twisted pair running from the sensor. Each wire is soldered to its respective pin on a 9 way D-type female serial connector.

[PMende.Wisc]

The wiring diagram may be seen in the attachment.

[JasonSmith]

That is strange. Their datasheet clearly states RS-422, but their wiring diagram is clearly not RS-422. Given that they are telling you to connect it to the DB-9 on a computer (And your experience that it actually works that way), it seems that this is really a RS-232 interface and their datasheet is inaccurate. I would tell you that it should work with a PXI-8430 RS-232 interface, but you are likely to encounter issues at some point with the 500 feet of cable, as this really is abnormal for RS-232 communication.

One option would be for you to use your PXI-8431 interface, then use a third party RS-422/RS-232 converter close to your sensor. This would then allow you to use a long run of cable. Just make sure that the converter you use has its own power supply, as the ones that try to leach power from the serial port are not always reliable.

Of course I would probably start by contacting your vendor and questioning them why there isn't actually a RS-422 interface on the sensor. Maybe they sent you the wrong part. 

-Jason S.