Alternate PID removed in 4.0?

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BrunDog
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Alternate PID removed in 4.0?

Post by BrunDog » Sat Apr 04, 2015 1:22 pm

Hi guys,

Just got my BCS and I am looking to control one output with two different PID tunings. This is because I want to control a RIMS with different settings for mashing (and 120V) and sparging (at 240V). I would like to change the PID tunings on the fly, and I thought that one way to do it was to physically tie two outputs to same SSR, and just use the appropriate output (and its associated PID parameters) at that time.

However, in firmware 3.7 there was an Alternate PID option, which if I understand it correctly, would have allowed me to do it with only one output (therefore not sacrificing one). Has this been removed in 4.0+?

-BD

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JonW
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Re: Alternate PID removed in 4.0?

Post by JonW » Sat Apr 04, 2015 4:20 pm

The actual tuning follows the output. Thus, if you want different tuning parameters, you'll need to use two outputs.

BrunDog
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Re: Alternate PID removed in 4.0?

Post by BrunDog » Sat Apr 04, 2015 4:38 pm

Thanks sir!

-BD

BrunDog
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Re: Alternate PID removed in 4.0?

Post by BrunDog » Sun Jun 21, 2015 7:42 am

Lesson learned on this for any who follow suit...

You cannot tie two outputs together and use that combo to drive the SSR... not exactly sure why, perhaps the pulldown resistors in each output are strong enough to reduce the voltage to below the SSR input threshold. When both outputs are on, the SSR will be on, but with only one or the other on, the SSR will not be. I resolved this by using the other half of a DPDT relay that was already being used for the high voltage side of the circuit in my design.

-BD

Ihop2many
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Re: Alternate PID removed in 4.0?

Post by Ihop2many » Sun Aug 16, 2015 12:47 pm

You cannot tie two outputs together and use that combo to drive the SSR..
I am brand new to BCS programming (just got my 462 yesterday) but see no reason why you cannot tie multiple outputs to an SSR or other DC controlled devices without issue. The clue is to stop the various outputs "seeing" each other. You would do this by putting a diode into the output terminal of the connector block and then soldering a wire from the other side of that diode to your SSR. Each output that is going to share a common load would have to have a diode in series in the output path. The diode stops the voltage of one output going to another output due to its high reverse impedance. You must have the diode in the correct polarity otherwise nothing will flow, fortunately this is easy to configure: when a diode is inserted correctly the voltage across the SSR will equal 5V, if reversed the voltage will equal 0V.

I was using this technique more than 40 years ago with mechanical relays, it worked then so should work now.

Hope this helps,

BrunDog
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Re: Alternate PID removed in 4.0?

Post by BrunDog » Wed Aug 19, 2015 6:05 pm

You may be right - this could potentially work. Keep in mind diodes have about a 0.7 V drop across them, but that may not be enough to matter (SSR should trigger at 4.3V).

I will test this and report back. Thanks for the idea.

Of course this does not fix the original request, so two outputs are still required, but it is still helpful.

-BD

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