Anybus AB7308 - power loss triggers unwanted action

Hi :slight_smile:
New here, I’m a field service technician (Refrigeration), and not an expert on automation or programming.

I have a question about the anybus AB7308.

We have a Saia PLC as the master/operator, the plc communicates Modbus tcp to the anybus AB7308 and the anybus AB7308 translates that to CANopen on a loop consisting of 24 eltorque valve actuators.

We are having some issues with setting this up properly, it’s on a ship, so we need this to operate safely and predictably.

What is happening is that we have 10 of the actuators in full open, if we loose power on the anybus AB7308 the actuators will close, then when the gateway powers back up the actuators go back to their previous position.
The same happens if we loose communication between the Saia PLC and anybus AB7308

For the safety of the ship and crew, what we need to happen is that if there is a loss of communication of loss of power is that the actuators stay in the position they were in.

I’m used to modbus directly from the Saia PLC, where nothing happens unless there is a user input. the PLC sends out a “goto_pos” signal to an actuator, the actuator goes to that position, after that the Saia PLC is just scanning the bus asking “are you there?” and “what is your position?”

The anybus AB7308 seems to first send out a “goto_pos” and then it either has to keep saying “stay… stay… stay…” to keep it there, or it detects that it is loosing power and sends out an “everyone back to zero” signal before it powers down.

What we need is for the anybus AB7308 to not do anything other than translate.

I’m on site, the client is not happy with the delay and our PLC guru has been trying to reach someone from HMS for two weeks that has in depth knowledge of the product who can help him set it up, or tell him if it’s possible at all with the anybus AB7308.

Looking forward to hearing from any of you :slight_smile:

Best Regards


I think what might be happening here, is that the Anybus is reading values cyclically (say every 100 milliseconds, for example), not just when they update. Is the transmission type Cyclic, Sync? If so, try changing that to Acyclic, Sync to see if that solves the issue.

Try that first and let us know what happens.

Hi Kyle,

Thank you for you quick response :slightly_smiling_face:

And thank you for your educational answer!

To explain, the PLC will send out a “are you there?” and “what’s your position” question to all the actuators constantly…


Saia PLC: Hey gateway, ask 1 if he is there, also ask him what his position is and report back to me --> gateway: 1… are you there? ok… what is your position? 50% ok, cool. -->Gateway to Saia PLC, 1 is there and at 50%

Saia PLC: Hey gateway, ask 2 if he is there, also ask him what his position is and report back to me --> gateway: 2… are you there? ok… what is your position? 75% ok, cool -->Gateway to Saia PLC, 2 is there and at 75%

Saia PLC: Hey gateway, ask 3 if he is there, also ask him what his position is and report back to me --> gateway: 3… are you there? ok… what is your position? 35% ok, cool -->Gateway to Saia PLC, 3 is there and at 35%

You seem like someone who knows what you are talking about!

I will forward what you have given me so far to our PLC guru :slightly_smiling_face:

Is there any way I can put our PLC guru in direct contact with you, because I’m just a field service technician speaking binary in a hex world


Here’s the thing… the website is run from the Americas region (we cover North, Central, & South America). Your support office is in the EU (Sweden in your case), so you would need to call someone there, +46 35 17 29 56. You can also open a case at and someone should contact you from that office. However, we’ll do our best over the forum to assist you in the meantime, we just can’t work with you outside that channel unfortunately.

Hi Kyle, you are a champ!

As with all things, we need an answer as soon as possible, because we have a client that is not happy

Our PLC guru has gone through contacting the main office in Sweden by using the contact feature on the web page, that creates a support ticket, and then he has to sit there and not getting anything done until that ticket was picked up…

The answer he got from sweden was:

(translated from swedish to english)

Hello ,
Received a reply late yesterday from a colleague.
As it currently looks, this is how the gateway works.
Without more extensive testing, which under current circumstances we cannot initiate, we have no work around for the problem.

To me, that seems like an answer from someone that has been left on “e-mail duty” who doesn’t have knowledge of the product like you do.

Maybe our PLC guru lacks initiative or google-foo, I don’t know… I found HMS.howas my first result on google when I searched for “anybus resets output when loosing power”

Just to be clear, no hard feelings, you are unable to lend me any further support, because I am in Norway, and you are in the US?

:slightly_smiling_face: where is the spirit of the company, the togetherness of HMS, everyone pulling together towards a common goal of making HMS better, global support available to everyone, to make sure that HMS has 24/7support

I mean, like I said, I am a field service technician, but it was instantly clear to me when I got your first reply, that you know the Anybus AB7308 and that you are not just someone that has “dabbled with it” or has “played with it from time to time”

You have USED it and know how it works :slightly_smiling_face:

I am very thankful for the advice you have given so far!!


What I’m saying is that you need to go through the Sweden for direct support, like telephone support. We support the forum and have many customers in our region who we must support directly as well. If you want to continue to ask questions on the forum we will continue to answer and do our best to help!

Do you have the config file (.cfg)?

Hi Kyle, here is the config file.

this is with 3 actuators for testing.


AnybusConfig_17042020.hcg (45.4 KB)

The transmission type in your config is set to Async. Was that recently changed or has it been set this way when you were experiencing the problem?

No, this is the way it has been set since the beginning.

Should this be changed, and can you point me to where this should be changed?

No, the setting is correct. Also, I was assuming the PLC was losing power, but it sounds like the AB7308 itself is what’s actually losing power, at which point we have no control over what the actuators do, our device is no longer online. In other words, the actuators are not being told to close by the AB7308, they are doing it on their own.

The solution would have to be with the actuators themselves, or solving the power loss issue.

Hi Kyle,

Just got a final piece of information.

The valves don’t close when it looses power. what happens is that when the Anybus gets power it goes to “pre-operational” and the valves close, Once it is in “operational” they open again.


No I/O data is exchanged when the device is in the pre-operational state.