RS485 connection to ESPEC climate control chamber

[k_tunsten]

Hello all,

I'm having some difficulties setting up and RS485 link with a climate control chamber from ESPEC. 

It is an ARL-0680 climate chamber. The climate chamber has two male DB9 connectors on the outside, apparently used for linking multiple RS485 chambers together. 

The pinout of the DB9 RS485 intrerface connector is: 

1:   SD+   Transmission data (A)   Connected

2:   SD-   Transmission data (B)   Connected

3:   RD+   Reception data (A)   Connected

4:   RD-   Reception data (B)   Connected

5:   GND   Ground   Connected

6:   GND   Ground   Connected

7:   NC    (Not connected)   Not connected

8:   NC    (Not connected)   Not connected

9:   NC    (Not connected)   Not connected

I have bought a NI USB-485 interface cable. This cable also has a male DB9 interface but the pinout is different. 

1:   GND

2:   CTS+ (HSI+)

3:   RTS+ (HSO+)

4:   RXD+

5:   RXD-

6:   CTS- (HSI-)

7:   RTS- (HSO-)

8:   TXD+

9:   TXD-

So - the pinouts do not match and I see different signal names on both interfaces.

Am I correct in assuming that I should only make the following connections:

NI USB485   to   ESPEC climate chamber

   1                       5, 6

   2                       not connected

   3                       not connected

   4                       3

   5                       4

   6                       not connected

   7                       not connected

   8                       1

   9                       2

Are there some special things I need to do in SW to get this setup to work? I'm using LabVIEW as my programming language to try and control the climate chamber. 

I'm especially not sure how I need to set up the transceiver mode to get everything working...

In the ESPEC documentation I could find that the communication system used is "Synchronized modulation (four-wire, half duplexing)".

Thanks a million for all your helpful feedback!

K.

[K C · Accepted solution]

You connected Rx to Rx and Tx to Tx.

You should connect Rx to Tx and Tx to Rx. In this way you create a four wire interface. You should set your board (in MAX) also to 4-wire.

To make it perfect you should also connect a 120Ohm resistor at each end of the balanced line. So in total 4 resistors.

If you want I can draw you a picture to replace these (1k) words.

Kees

[k_tunsten]

Thanks Kees - a picture would be helpful for me - I have to admit that I have no experience at all with RS485.

Thanks for your help!

Kirsten.

[k_tunsten]

Thx - it is working now....

[K C]

Here it is.

You should check your device if it already has termination resistors. You don't want two resistor at one end. So either use the resistors at your device or add them yourself as shown.

I think that your USB device has no termination resistors.

Kees

All my work for nothing  Kudo's

Glad it is working.

[ShellTox]

Hello

I've been web searching for some time, but this is the only forum that have a reference to ESPEC and RS485 I could find.

I'm trying to communicate with an ESPEC MC-811P thermal chamber with a RS485 interface.

I'm using a Brainboxes USB to RS485 converter and then connect this interface to the chamber with a cable that I've assembled.

From the specifications document from ESPEC, and from the datasheet from Brainboxes the pinouts follow:

USB to RS485 converter                    Thermal Chamber

1 TXD-        Transmited Data -            1 SD+        Transmission Data A
2 TXD+       Transmited Data +           2 SD-         Transmission Data B
3 RTS-        Ready to Send-               3 RD+        Reception Data A
4 RTS+       Ready to Send 6             4 RD-         Reception Data B
5 GND        Ground                           5 GND       Ground
6 RXD-        Received Data -              6 GND       Ground
7 RXD+-      Received Data +             7 NC          Not Connected
8 CTS-        Clear to Send -               8 NC          Not Connected
9 CTS+       Clear to Send +              9 NC          Not Connected

In the cable I've made the follwoing connections:

TXD -        RD -
TXD +       RD +
GND        GND (5 and 6) (cable mesh)
RXD -       SD -
RXD+       SD +

All the other pins are not connected

I've also added 4 120R resistors between TXD- and TXD+, RXD- ad RXD+, RD- and RD+ and finnaly SD- and SD+.

As a first approach I'm only trying to send commends and receive answers from hyperterminal, but after this I will use Labview to automate the chamber temperature readings. I'm trying to read the chamber conditions and I'm using the command 1,MON? with hyperterminal, but I get no answer.
The chamber is configured with
Address 1
9600 baud
Parity None
Delimiter  with CR and LF
Data Bits 8bit
Stop Bits 1bit
Protocol Stnd
Echo Back off
Data Length 7
Stop Bits 1

Can you detail how you managed to communicate with the chamber, please?

[K C]

Hi,

Is your USB device suitable for 4-wire RS-485 ?

Some manufacturers reverse the + and - of the RS-485 connection (don't ask me why) maybe you can try this.

Kees

[ShellTox]

Hi KC

Thank you for your reply.

The USB to RS485 converter datasheet states the following:

I think that being able to communicate in full-duplex it must support 4-wire RS485.

I've read about that sometimes the + and minus are revered. Thinking on that I've tried the 4 different combinations. None of them worked

The combinations are:

First

TXD -        RD -
TXD +       RD +
GND        GND 
RXD -       SD -
RXD+       SD +

Second:

TXD -        RD +
TXD +       RD -
GND        GND 
RXD -       SD +
RXD+       SD -

Third:

TXD -        SD -
TXD +       SD +
GND        GND 
RXD -       RD -
RXD+       RD +

Forth:

TXD -        SD +
TXD +       SD -
GND        GND 
RXD -       RD +
RXD+       RD -

I also tried to debug the USB to RS485 converter with a null modem cable, first with the converter only and then with the cable I've assembled also. I was able to see echo on hyperterminal and I've noticed that TXD- transitions from Low to High (idle line state is low) and TXD+ transitions from High to Low (idle line state is high).

I'm not sure if I need the termination resistors, since there aren't any references about this in both datasheets (converter and thermal chamber).

I don't have any more ideas about this problem. I really would appreciate any help with this.

Thank you

[K C]

Hi,

Well I think your tried everything I can think of.

The baudrate in the picture is a bit strange. '921,600' But I am sure that you have set all the parameters as they should and double checked the settings.

The terminators should always be there. Yes short and/or slow connection work without terminators but there is a good chance that it will fail in the future.

Sam applies for the GND connection, but you connected that one.

I will think it over this weekend but at this moment I cannot think of what you did wrong.

Still one wild guess connect the TXD to the SD also with the two ways with + and - 

Kees

[ShellTox]

Thanks KC, for your time.

Still no communications.

About your suggestion, you mean connect TXD+ to SD+ and SD-? I'm not sure if I completely understand your idea.

Can you detail it a bit more, please?