I am using a Radix make 16 channel temperature scanner which communicates with host computer with RS485. I have used a RS485 to RS232 converter in between. The terminals available on the scanner are the following:
D+, D-, D+,D-, RS485 Ground

The teminals available on the converter are D+,D- only, and a 15 pin DSUB connector on the other side. I have connected only D+ and D- on the scanner to the D+ and D- on the converter. I connected the DSUB connector to the COM1 port on the PC.

I am using a proprietary Labview based utility provided by the vendor. But it says the device is not communicating.

Can anybody point out what is the mistake?
Also, is there a definite way of knowing if the com port is working or not?
Also, if I don't want to use the proprietary software given by the vendor what should I do?

 

Here's my two-pence worth (or 2 cents for the American audience).

1. Try swapping the D+/D- terminals over, - it only takes a few minutes, and in my experience different manufacturers have different ideas as to what should be 'plus' and what is 'minus' It won't hurt anything to try - it just inverts the sense of the signal.

2. You don't say what RS232 converter you are using. Some have dip switches to set the baud rate etc. These will need to match your software and the device you are talking to.

3. RS232 has separate wires for for transmit and receive, whereas RS485 (2-wire) only allows a device to talk or listen, but not at the same time. The difficulty with RS232 to RS485 conversion is knowing when to turn on the RS485 transmitters, and when to listen. There are normally 2 ways:
a) Automatic - the device senses when something is coming down the RS232 Tx line and turns on the RS485 transmitter.
b) Using the RTS handshake line.
- This is where things can come unstuck because not all software will control the RTS line, and the RS485 converter spends all its time listening.
- Some converters provide the option to select which way.

Additional information that would help in answering would be:
What model of RS232-RS485 converter you are using?
What protocol does the scanner use?

Hope this helps,

~Carl

 

Try

1. Jumpering the two D+ together, and connect it to the converter's D+ terminal.
2. Jumper the two D- together, and connect it to the converter's D- terminal.
3. Connect the RS485 ground to the converter's RS485 ground terminal.

 

If this doesn't work, keep the jumpering suggested in place and swap the + and - on the converter side. What you have is a 2 wire RS485 connection on converter and a 4 wire RS485 connection on the scanner.

 

Can I take these values directly on FTView SCADA??