On/Off Pump Control

[TerryJC]

So we'll need another one too.

[Penri]

Hello Terry

Can't the SSR signals share the same 0V as the supply, that's how its wired inside the twin SSR box?


Hwyl

Penri

[TerryJC]

Yes. That's what I was suggesting. For some reason I thought all four pins had been used. I only read the first part of your message.

[Penri]

Terry

Does that mean we're OK?, the SSR box is wired as per the cct diag "Twin SSR Circuit v04" which should be earlier on in this topic.


Penri

[TerryJC]

Yes, We'll still need to make the Mods to the SumpPi circuits that I suggested, but it seems that you've already covered the cable half of the Round Industrial connector.

[TerryJC]

Hamish,

I've attached a slightly modified SumpPi Flowchart, which now uses the decision box on the bottom right which was previously labelled 'Sump Level < 400 mm', but ended up with 'Do nothing'.

Now, the Main Circulation Pump will be turned off if the Sump level is below 300 mm and turned on if the level is less than 400 mm, but greater than 300 mm. There may be a more efficient way to do this, please let me know if you can see one.

[TerryJC]

Hmmm. Barely 5 minutes had passed after I uploaded the last file before I realised that what I had suggested was a bit simplistic and assumed that the reading rate was fast enough to catch the level as it passed between 300 mm and 400 mm after the Main Circulation Pump had been turned off. This is quite likely, but it would be better to be sure, so I've added another test to prevent the situation where the pump is switched off on a falling level, but not back on again as the level rises.

So. Now, the Main Circulation Pump will be turned off if the Sump level is below 300 mm and turned on if the level is less than 400 mm, but greater than 300 mm, even if the level change happens very quickly. There may be a more efficient way to do this, please let me know if you can see one.

[TerryJC]

Sitrep.

This morning we removed the SumpPi hardware and carried out the modifications. These were slightly different to what I had predicted because Penri had already wired the 4-pin round industrial connector to SSR2 on the outside and 0 V on the inside, so the mods to the Interfaces Board were:

• Move the SSR2 control wire (Green) from Pin 42 to Pin 44.
• Snip the wire between the 5 V supply and the top of the 10 k resistor.
• Add a wire between the 19 V supply and the top of the 10 k resistor.

I also removed the two 220 R resistors in the emitter of the two 2N3906 transistors. They were originally added to pull down the O/P when I thought that both channels were going to be driven from 5 V. Unfortunately, as we found on SSR1 channel, with a 19 V supply they dissipate 1.6 W, instead of the 113 mW with the 5 V supply. These were 1/4 Watt resistors! In fact, the pull-down function is adequately provided by a 1 M resistor across the input to each SSR.

After we had completed the Interfaces Board mods, we reconnected the box and tested the system with the old Single SSR switch. Both SumpPi and ButtsPi were observed to be working normally. We then removed the Single SSR and installed the Twin SSR. We tested that the Butts Pump came on at the right levels and checked that the Main Circulation Pump was operating.

Further testing requires the software.

[hamishmb]

Hi,

I shall just purposely always turn the main pump off if the level is < 300mm (whether it's 0mm, 100mm, 200mm or 300mm), and purposely always turn it on for every other occurrence, so there is no situation where it should have been turned on/off and misses the "gate" so to speak. This is what I currently do for the butts pump. Does that sound like it'll do what you want?

I don't know when the software will be ready because I'm particularly busy at the moment doing coursework and job hunting, amongst other things, but this is a simple addition, so with luck it should be soon. My priority though is trying to stop the river leaking, so most of the time I spend thinking about WMT is about that for now.

Hamish

[TerryJC]

I shall just purposely always turn the main pump off if the level is < 300mm (whether it's 0mm, 100mm, 200mm or 300mm), and purposely always turn it on for every other occurrence, so there is no situation where it should have been turned on/off and misses the "gate" so to speak. This is what I currently do for the butts pump. Does that sound like it'll do what you want?

OK.

My flowchart was simply implementing what Penri had suggested:

On the S/W front I was thinking that the circulation pump should switch off if the sump level drops below 300mm and back on when the water level goes above 400mm. This will mean that we have another sensor above (500mm) and below (200mm) each level should the 300mm and 400mm sensors go AWOL.

That is, Off at 200 mm and on at 500 mm.

Your suggestion will turn it off at 300 mm and on again at 400 mm. Penri, Do you think that this is enough hysteresis?