Modbus RTU problems CT Commander SK Drives

[protocolpacket]

Unfortunately there are many makers of equipment that happen to have an RS-485 port, and they install the termination for you

How TRUE !!

To test whether a device has built in biasing:
- power up device without connecting the device to a 485 bus
- go into idle mode - turn off the master's communication so that there is no on-going comm
- steady state voltage across the A & B lines should be greater than 200mV, typically less than 1 volt, but it can be higher.
- if there's no biasing, then steady state across A & B = 0V

My earlier findings….

1. Converter powered up not connected to anything the voltage between DATA+ AND DATA - = 4.9V DC , This is not about the local converter.
2. Voltage when the entire bus was connected and one drive was connected , no communication be initiated from master = 322 mv.

Can you connect a wire or the shield in such a fashion without drawing an arc?

I will leave the shield opened at all drives end, not connecting the shield to the 0v terminal block inside the drive or to the Body of the panel, or to the earth available at the drives panel. In effect what I am saying is I won’t be using the “Optional Link2” as shown in my earlier picture.

However I am letting the 0V inside the RJ 45 connector to come down to the converter end, still not connecting them to any end at converter ( Master) till I do what you have told me to check (the current on 100 Ohms resistor if any current flows).

I am not confident if I install the prefabricated cable with all the 0V of all the RJ 45 to get shorted , till I check this with each and every connection till the converter end .. why? because I don’t know what has been done inside the converter or the Drives and how good is the grounding at each end and each destination of installation.

Connecting that 0V to which point I will demonstrate in my Pic shown below. (This I will do as a last option) I know you won’t agree to that, as you would want me to go ahead with it…

Please see the PIC where I have marked as “ ?? I don’t know” . How as a user should I feel confident till the manufacturer of the equipment is specific with the terminology show as GND means it has been like this inside the box too, which I normally should not open or use multi-meter/ scope to check such basic issues.

I can do that and check again, AND if I have 1000’s of such devices then that is the cost born by me for buying this equipment or leave it to my guess work and work on trials and error basis where I am prone to blowing the IC’s inside my Main ( more expensive ) equipments if that end installation is not perfect with all its earthing.

If my alterations ( black ) as shown in the PICTURE is GND ( Ground) have I been a fool who paid extra for this isolation ???

I presume the panels that hosts equipments/devices is also grounded and if it’s a din rail mounted equipment does the electronics inside the any box automatically get connected to the potential the panel is at !!!!!( Good grounded or not is another issue)

The deeper I go the more confused I am with earth and ground !! 0v DC, neutral etc…and something called GND.

Routing.

Should I drill another hole on the body of the original equipment to ensure I do that ?

I would be happy to open up manual of most of the manufacturers and study how clear they are with respect what they say and what they do inside their BOX. Sometimes easy to say what kind of an engineer am I who does not have a scope.

My Job is not to sit at site and do R&D with a scope and do my installation because the manufacturer of various equipment have been casual about their own documentation.

My Job is to ensure that the process that the Customer asked me to get going works and produces his end products. PLC and automation Guy , why ??? Am I supposed to be an R&D branch of every piece of equipment I bought being an Integrator??

Would anyone like to hear from their grocery shop, that milk they bough was not good because the grass the cow ate on Tuesday was not good!!! Would you blame the grocery counter man, for not having a scope to check the Ph value before he sold a sealed packet to you…should we be having a PH meter poking at every packet I find in the grocery shop to ensure I bought good milk?? Am I being Mr. Been !!!

Yes,.. I will use a Ph meter when I am using that milk with some strange combination to make a special Italian dish that tastes same world over after my own distribution network supplies this packed cheese world over….Not when I want to just drink the milk….

Not that I am trying to justify why I don’t carry a scope every time, just that as an integrator I need to concentrate on better issues than doing this.

I have been off from site for 2 days due to some other issues, Dear Dan I shall come back to you with all details.

May god bless this Earth.

Sorry for my bad attitude....

Best Regards

 

[protocolpacket]

Thanks DAN,



You gave me a lot of insight to many issues. Sometimes in subtle ways too.



I did manage to solve one section of the installation, thanks to you.



The main killer is the common mode voltage and you bet never easy to resolve, I need some tips if you have any more, I have done it in a strange way. I myself don't like it



There are some more issues i would like to discuss if you would/could come. Else its ok.



And thanks to you too Peeter about Power supplies if you were talking about interrogation supply and some analogue signal supply if they have to be same on Zero OR on earth and then effetely what its signal GND does to communication GND and COMMON mode voltage



Dear Peter YOU are best on PID, I DO READ some of your posts and keep away as I know "The Guru" is here, and if i have time i would like to learn from you , if you would be more understanding about our weakness. With your experience in this field you could be the best Guru, but then i shall wait till you could be more calmer.. Hope some day.....when you don’t get angry just because all can’t be as good as you…that is why you are you..…



Dan, 3 wire 485 is best , But i would really like to know if this is always possible ( Existing equipments, and how we resolve it smartly) with all equipment supplier who do not think the same way as you do ?



Regarding Stubs, I too am having the same confusion as you have as it worked in one test and did not in another ….



BEST REGARDS

 

[juanmdx]

Hello,

I know this comment doesn't have anything to do with your thread, but I'm looking around and you are the only one that is working with something similar than I.

I'm working on a project where I need to control 3 Commander SK Drives, each of the drives control 1 motor, and the variations on the speed of that motor are given by the current drawn by two other motors.

What I'm doing is working with a Beckhoff PLC and connecting each of the Ammeters and Drives to it (through analog outputs and serial bus interfaces KL6041).

What I want is the PLC to tell each Drive which velocitiy to give to the motor via the Modbus RTU, but I don't know how to do this (or even if this can be done), or do I have to use the Control Cables on the Drives?

(I attach a really simple layout of what I want to do)

Really hope you can help me.

Thanks and BR

Juan