JLD634 - use relay as PV?

[tomocar]

Hello,

The outy setting on the JDL612 allows the option of using the PV value to drive the relay rather than the PID main (ssr) output. This is very handy for simple non-PID control as you can still read the SV on the lower readout and manually raise and lower the SV with the up and down arrows.

I can't quite figure out in the manual for the JDL634 if it can also do this - I would like to be able to. The outy function for the JDL612 looks to me to give you several different options for the main output (current loop vs. ssr, etc.) - but it looks like the PV always goes with the main output - and no way to get simple (non-PID) relay output driven from PV. Am I missing something? Is there a way to do it?

Thanks!
Tom C.

[tomocar]

Another way...?

All I really need is to turn the heater on and off like a thermostat (no PID needed), but use the ramp and soak to change the temperature settings over time.

I'd like to be able to see the SV on the lower display though, as well as change the SV manually with the up and down arrows... so maybe the simplest thing to do would be to set the P, I & D (and other) parameters so the main output is working pretty much in a simple relay mode. That is, no compensation - just full on until it hits the SV and then full off until it dips a couple of degrees below SV. That would work fine. In this case, what would be a good set of values for P, I, D, Ct, SF, & Pd?

Thanks!
-Tom C.

[Tech_Marco]

JLD634 only allow one type of major output: SSR, or relay, or 20mA. All JLD634 we imported are SSR type with relay to serves as 'event alarm' only. If you want to run relay as control, you can use the SSR output to control a relay instead. But I really don't see why would you do so, paying good money for the features but not using it.

[tomocar]

Thanks Marco,

it's not that I want to use a relay, it's that I don't want to have to mess with the PID settings. I need ramp and soak but not (necessarily) PID.

As I said in my 2nd post above, I can use the main output if I can just figure out how to set the PID values so they have little or no effect. What happens if I set all P, I, D settings to zero, for example... or what settings do you think I should use?

Thanks again,
Tom C.

[Tech_Marco]

Why not use "Auto tune"??

[tomocar]

Hi Marco,

Well, we've tried that and not liking what we get. This is for an art glass studio, and sometimes the equipment is running a process and sometimes it is "in use" where the doors are being opened and closed frequently (as people are putting things in or taking things out, etc.) So the AT does not seem to set the parameters well for both conditions. The glass artist I'm working with has worked in many other glass studios over the years and he says he's never seen the large over-shoot and under-shoot we are getting, and he thinks they either don't use PID or they have them set at some values that make it respond almost like simple on-off. So we'd like to try that and see what we get.

If I just set the P and the I quite low and the D at zero - do you think that would come close?

Now, a couple of new questions (sorry):
1. In manual mode, is thee any way to get the lower readout to show the SV temperature (and the up and down arrows to adjust the SV temperature) rather than seeing and adjusting the proportional percentage?

2. In ramp/soak mode is there anyway to skip ahead to a certain step. For instance if for some reason we cancel out of a process and later restart and want to bump ahead to where we left off.

Thanks again for all your help, Marco!
-Tom C.

[richiem]

I downloaded the 634 manual and it looks to me like you can use the unit as a simple thermostat, in the same way that the JLD612 can be used, by using the J1 alarm relay to control another relay that turns the heat on and off. I haven't used one of these so I may be way off base, but as I glean the stuff in the manual:
Set rd = 0 for heating.
Use the alarm 1 relay, J1, which is normally open (terminals 5 & 6).
Connect a power source for the second relay to either 5 or 6, then connect the second relay to the other terminal of the two.
Set the AL1y = 11 to disable the alarm hold function.
Set AL1C = to a hysteresis value you can live with, but at least 0.2 (= 2 degrees) -- in your situation maybe 10 degrees or even more ... glass furnaces are really hot, so maintaining even a 20 degree spread between on and off may be too fine a range.
SV has no meaning here since there is no internal control from the 634. PV will read the current temp as always.

See fig 2 in the manual on page 5

Hope this helps a little.

[tomocar]

Thanks for your good try - I've been all over that one, and can't use it because to set the set value for relay 1 you have to use PW 0001, parameter AL1 and then enter the temperature. That woks but then you can't see that on the lower readout, and you can't adjust it with the up and down arrows. So this won't work for us. We need to figure out a way to use the main output, so we can use SV and the lower readout.

Thanks again though - I appreciate that folks browse this board and offer help. I try to also from time to time.

-Tom

[richiem]

OK, Tom -- I hear you. I think you should try using the PID control, running the autotune on the system closed-door once the PV is within say 100 degrees of the SV. This will let the controller figure out the gain/loss rates over a few cycles, and set the appropriate params. Then when the door open/close business is going on, the system will try to regain control immediately. This mode will let you set the SV with the arrows. And you still have adjustable hysteresis if that helps....

Once you have the AT params established, then you can play with P, I and D values to see if you can improve response time. This would mainly be in the D value, and the overshoot param.

Of course, you could just use a regular industrial thermostat....

[tomocar]

Okay, great! Thanks so much - sounds like you understand PID pretty well!

I will give that a try.

Best Regards,
Tom