Electronic – Cannot establish serial communication from a sensor

rs485

I have the following wind sensor (RT240):
http://www.nrgsystems.com/FileLibrary/829de7ea934944f09798ad2830abfa65/RT240_and_RT20_Manual.pdf

It has a 8 pin connection cable and I'm trying to receive/send data from a PC by using "Full duplex pin assignment" at page 9.
I want to convert RS485 to RS232 for communicating with a PC.

The point is, I'm kind of lost between protocols and interfaces in this manual.
I'm trying to use RS485 interface and I have the following converter I-7520A (at page 14):
http://ftp.icpdas.com/pub/cd/8000cd/napdos/7000/manual/7520.pdf

If what I'm trying to do make sense, here is how I connected the connector pins to the RS485 converter:

enter image description here

Here is how I connected the cable connector pins to the RS485 converter:

Pink (RXD-) to 5 TX-

Yellow (TXD-) to 7 RX-

Red (Control con.) to nowhere

Grey (RXD+) to 4 TX+

Green (TXD+) to 6 RX+

Blue (Analog ground) to nowhere

White (Supply Voltage – ) to 10 and they the together to + of 24V DC

Brown (Supply Voltage +) to 9 and they the together to – of 24V DC

First of all, when I power the sensor and the converter I can’t hear any sound from the sensor where I supposed to hear tickling sound normally. It looks like it doesn't power up unlike the converter. And I also don’t see any data from the PC serial port by using Windows HyperTerminal.

I’m really lost, could anyone guide me how I can use RS485 interface with this sensor and convert it to serial. There is also SDI-12 protocol in the manual which I have no idea about.

What I was trying to do was to use RS485 protocol for this sensor and receive send data in ASCII format. Could anybody give me a little help? It looks like I'm doing something fundamentally wrong here.

Best Answer

Your sensor has some different modes of communicating:

  1. Modbus, a software protocol that can be run on the electrical standard RS485. Making manual Modbus frames on the terminal seem improbable.
  2. NMEA, combined software and electrical protocol/standard. Can be run on RS485 and others. Could probably be done on the terminal but it also requires some protocol frame building.
  3. SDI-12, combined software protocol and electrical specification. 5V logic levels. SDI-12 should be fairly easy to use with the terminal but you would need a SDI-12 to RS232 converter.
  4. Analog current/voltage. Directly measurable by an ADC or voltmeter.

You have to decide which one to use. I would test 4, first to see that the unit is in working order. Attach supply to pin7 & 8. One 1k resistor from pin 2 or 4 to ground. Measure the voltage over the resistor and see if i changes with whatever parameter was set in the factory:

"The analog measurement outputs are configured at the factory based on customer specification" //From the manual

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