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Old January 3rd, 2014, 01:59 AM   #1
unsaint32
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Omron E5CN temp controller control output type

My work has a temp control setup with Omron E5CN temp controller and an SSR. I am not sure what type of control output it has. (relay, voltage, current output) I know it's E5CN. So, here is my question... The manual shows different output types of the temp controller. Do certain models come with specific output types, or is the output type something I can configure?

The one at my work has L1 to one terminal of the output contact, and SSR to the other terminal of the output contact (as if the control output was just a contact that closes when the PV is below the SP). So, that tells me that the control output is a relay type. But then why SSR? Why not connect the contact directly to the heater?

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Old January 3rd, 2014, 09:47 AM   #2
danw
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1) The world of controls is the world of model numbers. Model numbers define what a specific unit has for hardware and firmware features.

So, do a Google search for manual or spec sheet for an Omron E5CN that has the model selection guide:



So what kind of output(s) does your unit have?

2) As to why one does not connect the relay output directly to the heating elements, the 'switch' (the relay contacts) has to be rated to carry the current load. Too much current burns relay contacts.

The Omron's internal relay can handle 3A.

How many amps do your heating elements draw? My toaster at home draws 12A.

Last edited by danw; January 3rd, 2014 at 09:50 AM.
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Old January 4th, 2014, 05:43 AM   #3
unsaint32
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Thanks Danw for the very helpful reply. I checked the model numbers of those at my work. They are all relay output type. And they all use SSR. So, my next question is why SSR? If the controller output was voltage or current output type, then I can see that the SSR can use the analog input. Why not just use a simple relay as long as the relay contact can handle the load current? The relay would open and close just as much as the temp controller's relay output, right?
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Old January 4th, 2014, 10:36 AM   #4
danw
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Relays are electromechanical devices which means that they have moving parts. The moving parts wear out and break. Relays are rated for X cycles, which could tens of thousands, hundreds of thousands, may be even millions, but the point is, eventually they're going to break.

A solid state relay has no moving parts. It can switch millions of cycles and continue to function, as long as it is installed properly, meaning that it has an adequate heat sink to get rid of the wattage that drops due to its internal resistance (I^2R loss).

Keep an SSR well bonded to a heat sink and supply some cooling air and it'll run forever, or almost forever.
Relays on the other hand, die fairly (relatively speaking) rapid deaths.

Solid state relays (little rectangular bricks) come in two versions, one with a low voltage on-off input , usually something like 3-30Vdc, the other with high voltage on-off input, 115 or 230 Vac.


If your SSR's use the low voltage input, 3-30Vdc, your plant would benefit from using the Omron's Q voltage output (for driving SSR), which is a solid state device, because the controller's solid state output hardware would last longer than an electromechanical relay. Omron's Q voltage output is an on-off output, not a continuous output like the what Omron calls "current".

Analog current (0-20mA, 4-20mA, 0-1Vdc, 0-5Vdc, 0-10Vdc) outputs are not useable with SSR solid state relays which are looking for an on-off input signal.

The other kind of SSR's (also called thyristors) have a larger physical format, always include heat sinks, typically run on 3 phase and use a continuous analog input control signal. They look like this:
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Old January 5th, 2014, 12:01 AM   #5
unsaint32
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I see. So, even with the heat issue, SSR has better longevity. I always thought of SSR as a more accurate way of controlling temperature by altering its output sine waves proportional to the input signal variable, which leads me to my next questions.

Quote:
Originally Posted by danw View Post
Analog current (0-20mA, 4-20mA, 0-1Vdc, 0-5Vdc, 0-10Vdc) outputs are not useable with SSR solid state relays which are looking for an on-off input signal.
I thought there were two different types of SSRs: one type that takes on/off signal input and the other type that takes analog signal input that determines the proportional control output.
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