Adding an ORP to the LQ

[Rabbit]

So I've been thinking. It would be really simple to electronically control the output of the LQ with an ORP driven solenoid valve. Well when I say driven I really mean that the ORP would be the deciding factor to open or close the valve. The ORP would be compared against a percision reference voltage with a basic comparator with a bit of hysterysis. It would turn on at a low point and turn off and stay off once it hit the high point. If the low point was reached again it would turn back on and repeat. The amount of hysterysis would set this window. This would prevent the solenoid from turning on and off too frequently.

Such a control mechanism could have two controls, one for the high point and one for the window of variation desired. A basic power transistor or even a Mosfet could be used to drive the solenoid. Some other support components would be needed to ensure no electrical noise or kick back from the coil. This may be beyond the scope of most in this forum.

I could also see the LQ still having it's control mechanism in place to help prevent complete over chlorination in the event something got stuck. The output could be set to say a bit higher then normally needed to maintain.

Ok, so I just need to find a cheap (inexpensive) ORP sensor and a solenoid valve that'll last in the harsh environment. The rest is cake. I've prototyped and built countless small and large circuits to do various tasks. This sounds like a useful one.

I've checked on the net, I'm only finding pretty pricey ORP sensors. I'm wondering if anyone has any sites that might have some reasonably priced ones.

 

[JasonLion]

ORP sensors seem to start around $70 and ones that are of known high quality tend to cost around $200.

The differential amplifier to read the signal from an ORP sensor is a little bit tricky to get right, towards the high end of the advanced amateur range. You might be better off going with something like the HANNA BL932700-1 ORP minicontroller.

 

[duraleigh]

Rabbit,

A year ago, I was trying to "invent" a chlorine applicator similar (but simpler) to LQ.

One of the criteria was that it not need any other source of power than the pool pump. That would make it affordable and less complex for those folks who didn't have a convenient source of power near their pump.

That restriction eventually led to me giving up on the device.

Adding power, as you are suggesting with the ORP opens up a lot of new possibilities and could probably be done with something simpler than LQ.......say maybe a straight chlorine dispenser with a peristaltic pump.

Your thoughts are interesting but, like you said, I think it will be beyond the scope of what most of us can do as DIY. Once the overall cost approaches somewhere around 70% of an SWG, I think most folks (me included)
will go for the SWG.

 

[Rabbit]

Your thoughts are interesting but, like you said, I think it will be beyond the scope of what most of us can do as DIY. Once the overall cost approaches somewhere around 70% of an SWG, I think most folks (me included)
will go for the SWG.

Well I think it can be done for more around 70% of the price of an LQ. I'm slowly finding some ORP sensors in the $70 range. Just trying to find the right one, pipe mountable. One advantage to using the LQ over a peristaltic pump is that at least in my case the LQ is taking a ton of the salts out of the chlorine. If the circuit fails (unlikely) you still have a perfectly good means of chlorinating your pool.

In the long run I may want to go with an SWG and a digital control system. I'm a bit in a pickle however with my TA from the tap being 120. I would have to always be adjusting the TA. The LQ so far has been working wonderfully, well after I got the flow to a good enough level.

 

[duraleigh]

Rabbit,

It'll be interesting following your progress....please keep us posted.

 

[Guest]

I'm a bit in a pickle however with my TA from the tap being 120. I would have to always be adjusting the TA.

My TA from the tap is 130 ppm and keep my TA between 70-90 ppm with my SWG. I need to adjust my TA perhaps once a year. Not a bit deal.

 

[randytsuch]

A little while ago, I was thinking about adding an orp sensor, and asked sensorex about it,

They responded with this
We have shipped tens of thousands of ORP electrodes this year, for the pool and spa industry.
The part number to use is our S550C-BNC…..$75.00 each
(same as our 970884).
This is a 12 mm diameter x 150 mm long epoxy body with extended pure Platinum tip.
30” cable and BNC connector is standard.
Longer cables and special connectors are available at optional costs.
http://www.sensorex.com/support/specifi ... Pspecs.pdf

This sensor will work with virtually any make and model pH/ORP meter, transmitter, or controller.
You can place it directly in the 2” main flow stream if you like.

Be aware that an obp sensor is a specialized battery, so it will last about 2 years before you have to replace it.

BTW, I may still do this one of these days.

Randy

 

[Aquaman95]

Despite what some may say, you do not want to tap the ORP sensor directly into the main line. There is too much turbulence and you will not get accurate readings. It also increases the chance of the electrode getting broken. They are fairly fragile.

Build a bypass out of PVC or buy a commercially available sample cell.

 

[randytsuch]

Despite what some may say, you do not want to tap the ORP sensor directly into the main line. There is too much turbulence and you will not get accurate readings. It also increases the chance of the electrode getting broken. They are fairly fragile.

Build a bypass out of PVC or buy a commercially available sample cell.

So you think sensorex gave me bad advice?

I specifically asked them if I could put the sensor in the main, because I saw on commercial models they had put the sensor in a bypass line.

Randy

 

[Rabbit]

I had another thought. The ORP could go inline with the feed of the LQ. This of course would require constant flow through the LQ. So the solution would be to use the solenoid valve to increase the flow when needed as opposed to turning the LQ on and off. It would be more of a high and low setting. This would keep water running past the ORP at a slow safe rate. I figure just mount it in a 2" PVC pipe with both ends capped and threaded with barded inserts to allow the LQ to just connect right up.

 

[Rabbit]

ORP sensors seem to start around $70 and ones that are of known high quality tend to cost around $200.

The differential amplifier to read the signal from an ORP sensor is a little bit tricky to get right, towards the high end of the advanced amateur range. You might be better off going with something like the HANNA BL932700-1 ORP minicontroller.

They have a lot of low noise comparators that can handle mv ranges without problems. The biggest issue would be to make sure the noise is very low. Good power supply filtration would be a must. Still I don't see it as being too difficult. Some better quality components would be desired.

 

[Aquaman95]

Despite what some may say, you do not want to tap the ORP sensor directly into the main line. There is too much turbulence and you will not get accurate readings. It also increases the chance of the electrode getting broken. They are fairly fragile.

Build a bypass out of PVC or buy a commercially available sample cell.

So you think sensorex gave me bad advice?

I specifically asked them if I could put the sensor in the main, because I saw on commercial models they had put the sensor in a bypass line.

Randy

Technically they're right, but you will not get optimum results. I'm sure the potential sensor damage isn't much of a concern to them...they'll just sell more sensors.

Years ago most controller manufacturers didn't offer or include a bypass with their systems. I think everyone does now and it's with good reason.

 

[Water_man]

I'm sure it would be fun to design and build but for most of us, is it worth the time and the energy? I think if something may go wrong it would be WS blockage. I've had my LQ running for two months now with WS in the outlet line and pool FC level has been steady between 5 and 7. I'm sure there are others with similar performance, so why do we need a smarter control system?
How would your control system solve a flow block if the line cannot respond to a call for increased flow? The chance for this to happen is a lot higher than over chlorination.
My approach is "look for the lost key where you think you dropped it, not where there's more light." Let's solve the main problem of the LQ first and after that, automatic control would be the cherry on the icing of the cake.

Now since you're in a flow control mood, how about automatically lowering the pH at the LQ's top water level using a pH electrode and a dilute acid delivery system into the "In" line in order to prevent WS formation?