Controlling SSR with 2408

I'm looking to control a SSR with 3-32 VDC input in a heating application.

I have a 2408 with a changeover relay but I don't think this will work.

What module and settings do I need to configure to have a DC output to control a SSR?

Any help would be appreciated!
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  • Bob Anderson (Technical Support Engineer) February 19, 2018 08:16
    Hello Alex,

    You require a Logic output.

    This can be purchased from your local Eurotherm office.

    Part number :- SUB24/LO

    Please contact them for prices.

    Many thanks.
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  • Thanks, Bob.

    I see a SUB24/L2 (AH025278U002) listed but not a SUB24/LO? Can you tell me the difference between these?

    Thanks again!
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  • Bob Anderson (Technical Support Engineer) February 19, 2018 16:41
    Hello Alex,

    Certainly:-

    L2 is Non-Isolated Logic Output.

    LO is Isolated Logic Output.

    Kind regards

    Bob
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  • Thanks Bob!

    Sorry but I'm new to controls. Assuming noise wasn't an Issue, would non isolated work the same as the isolated version to drive a SSR?

    Thanks
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  • Bob Anderson (Technical Support Engineer) February 20, 2018 08:02
    Hello Alex,

    Yes the only difference is one is isolated, they will be the same.
    Isolated output can help if you have any potential differences between one device and another, but many applications run with non-isolated outputs to an SSR.
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  • Dear Bob,
    I am extending this conversation. I also recently got eurotherm 2408. I got this for two types of output control (Relay 2 pin: "R2 Fitted unconfigured") and (DC analog control "D4 Fitted unconfigured"). I have also 3- 32 V dc input relay already to control the heater output. I don't have much knowledge about "change over relay". Do you think with the (Relay 2 pin: "R2 Fitted unconfigured") can be used for controlling the heater via SSR?
    Thanks in advance.
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  • Jon (Official Rep) October 30, 2019 22:14
    Dear Debasish,
    If you had a 24v dc in the panel you could use the relay contact to switch the 24v to drive the SSR input signal or you could also configure the D4 to give out a permanent 10v output, then use the relay to switch the 10v to drive the SSR input.

    You would need to make sure that the cycle time on the relay is not too fast (5sec) to make sure the relay contact doesn't ware out to quickly.
    Thanks, Jon
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  • Dear Jon,
    Thanks for your reply. Just to make more clear I am asking few questions. From 2408 datasheet, for 2 pin relay it is written "Min: 12V, 100mA dc. Max: 2A, 264Vac resistive ". I was thinking it can be configured as dc output and as I have 3 to 32 volt control SSR. It should be fine to control SSR using 2 pin relay type. Am I right or anything else is there? Another question regarding the "cycle time on the relay is not too fast (5sec) " this, sorry may be I understood in wrong way. Is the minimum duration of including switching on and off for the relay 5 sec? Our goal is to maintain the temp ramp around 1 K/min to a certain temp. Do you think chances of noise will be more or PID will take care it? I am new in this kind of PID system. May be I am asking stilly question.

    Thanks, Debasish
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  • Jon (Official Rep) November 04, 2019 14:12
    Dear Debasish,
    Unfortunately, the relay spec's are what can be passed through the relay, it doesn't generate the voltage I'm afraid. You will have to do as suggested above.
    As the relay is a mechanical device, it can ware prematurely if it is switching too often. Setting the minimum on time will help in this regard.

    Thanks, jon
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  • Dear Jon,
    Thanks for your reply. Based on the above suggestion "D4 to give out a permanent 10v output, then use the relay to switch the 10v to drive the SSR input.", I have a few questions. Right now I set the D4 as dc output and upper limit as 10 volt and lower limit as 0 volt. Is that the way to give permanent 10 volt dc output for controlling SSR? It seems based on the setpoint value it will apply 10 volt or 0 volt but for D4 type terminal it is supposed to be continuous dc out. I mean it supposes to give any dc output between 0 to 10 volt based on the controlling condition. Am I right or it should give either 0 or 10 volt.

    Another quick question. I set this out put as OP-1 and function as "heat". But when set point is below the PV, OP-1 is on (flashing) and voltage is 10 volt and when PV is above the SP, OP-1 is off (not flashing) and voltage is 10 volt. I don't understand why it behaves in a reverse way. If you have any suggestions, please help me.
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  • Dear Jon,
    I am waiting for your reply. When you have time please update me on this.
    Thanks, Debasish
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  • Jon (Official Rep) November 07, 2019 22:17
    Dear Debasish,
    Ok, go to config>Inst>Ctrl & set to 'PID' > Act to 'Rev'

    Set the DC O/P to Heat / ValLow=0 ValHigh=100/ Out Lo=100 Out Hi =100

    Also, config the Relay to Heat / ValLo=0 Valhi=100 / Out Lo=0 Out Hi=100

    Exit config, and hopefully it should be working correctly.

    Jon
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  • Dear Jon,
    Thanks for your suggestion. I did this settings "go to config>Inst>Ctrl & set to 'PID' > Act to 'Rev'", it is working fine.

    Thanks for that. Regarding, "Set the DC O/P to Heat / ValLow=0 ValHigh=100/ Out Lo=100 Out Hi =100", I can't set it as "Out Lo=100 Out Hi =100". It has a limitation as Out Lo=0 and Out Hi=10. Anyway, I did this modification as "Out Lo=0 and Out Hi=10", right now at the OP-1 (dc-op), it is giving continuous voltage between 0 to 10 volt based on the PID. But not "permanent 10v output" as you initially mentioned for SSR triggering. I am assuming, it is supposed to be 0 volt or 10 volts. Please help me on how to make it as constant 10 volts or 0 volt.

    Regarding "Also, config the Relay to Heat / ValLo=0 Valhi=100 / Out Lo=0 Out Hi=100". I don't understand actually. I mean In my 2408 model relay is at OP-2 (2A), even if I change relay settings there, how it will help to control dc output of OP-1?
    Can you please explain this. Sorry for asking you multiple times, I did not get actually.

    Thanks,
    Debasish
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  • Hi Debasish,
    sorry Jon that I hop into your conversation.
    Jon told you this solution because of your actual hardware:
    one Ralay- and one DC-OP- Module.
    The DC-OP has to be set to constantly 10 V => Out Lo: 10 ( V ), Out Hi: 10 ( V )
    No matter what the PID OP says ( 0...100 % ), there will be 10 VDC at the terminals.
    You have to wire one of these 10 V legs to one of the Relay terminals, the other contact of the Relay to the SSR.
    Now the Relay controlls the SSR by switching the 10 V to the SSR On and Off.
    But you are always limited to the Relay which is a mechanical switch. It should not be faster than the 5 sec, even slower.
    Depending on your type of furnace I believe you are not able to establish the very slow heating rate of 1 K/ min with this kind of solution.
    The best would be to get rid of the Relay- and DC- Module and to put in a
    Logic-OP-Module, Heat, 0...100 %, 0...100 %. Connect it directly to the SSR Input.
    Now you can controll the OP as fast and accurate as possible without the machanical limitations of the Relay, and usually sensitive enough to establish the
    1 K/ min.
    I do hope this is helpful in adition to Jon's statements.
    Rudi
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  • Dear Rudi,
    Thanks for your reply. Now I have a clear picture based on what Jon suggests initially and your suggestions.

    Actually, we have a manually adjustable up to 30 volt dc power supply which supposes to power the heater and this outer heater circuit's on/off will be controlled by solid-state relay. And relay will be controlled by the 2408. Initially, I thought this relay port (R2) will provide the voltage to SSR. But based on all these discussions, it seems I was supposed to get a logic type o/p module in this case. That was my mistake. Today, I realized that this (R2) module has an internal relay. So, in that case, I can directly connect this relay port (for my case 2A and 2B) to the heater circuit for controlling the heater without using SSR. I did this. It seems working fine for me. My question is that idea fine or do you have any other suggestions on it?

    Another thing, I noticed that the internal mechanical relay switching on and off quite fast, I mean not 5 seconds delay. Roughly once or twice in a second based on the PV and SP conditions. I am not sure this much fast will able to make good control for 1K/min. or not, as you suggest.

    But do you think for the slow rate of heating, if I optimize the power (by lowering the voltage) of the dc power supply for the heater will help to reach the 1K/min. even if the relay switching rate is not so fast?

    Last question, for now, we don't have the logic o/p module. If we want to install it in the future, do we need to send the Eurotherm 2408 to the company for internal installation or we can separately buy that particular module and can install it ourselves?

    Thanks to both of you to make me a clear idea.

    Regards,
    Debasish
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  • Hello Debasish,
    without knowing the furnace and the application you are running it is allmost impossible to answer your questions. I just can give some suggestions or hints.
    As a matter of fact the Relay is the weakest part of your controlling. We claim something like 2 Million switching cycles. That sounds a lot. But if you calculate just one switch a second it is not too much. And the rating is 2 A maximum. Please check how many Amps your heater is consuming.
    You easily can change the modules by yourself. You already have done some configuration work ( Software ), to change the Hardware is not a big thing.
    Hope you can make it work well.
    Rudi
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  • Dear Rudi,
    Thanks for your suggestions. I got your point. And Yes, I checked the current rating for heater. It is 1.7 A. It should be fine. Let me assemble it in full system. I will update about the results.

    Just for query, can you suggest some model number for the module or what is the roughly cost?

    Another quick question, if we can get an analog control power supply, I think that will be the best option for controlling temp through dc output port that we already have.

    Thanks for your suggestions.

    Regards,
    Debasish
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  • Hello Debasish,
    Just ask for an "Single Logic OP Module ( non isolated )" for a 2404.
    The pricing depends very much at the country you are from. Please get in contact with your local Eurotherm.
    An analog control power supply working with phase angle controlled with the DC-OP-Module would be the best ( and the most expensive ) solution.
    Rudi
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  • Dear Rudi,
    Thanks for your suggestions.

    Regards, Debasish
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