Help with ORP and Salinity Circuits

Is your problem what sensor to use or how to provide 12vdc to your existing sensor shield? The Arduini Mega has a pin, Vin, which is the input voltage. Since you are powering the Mega with 12VDC, your shield will be able to use that voltage for your sensor. You just have to ensure that the inputs and outputs are 5v. Supporting circuitry may be needed for this.

Edit: I see you need 9v; easily derived from the 12v supply

Jorge Ramalho said:

Interesting what you've said. Almost ORP all circuits I have analyzed work with probes which measure range is 0 to +/-2000mV. All circuits have the same configuration as pH circuits: usually 2 opamps in series: one for the slope and the other for it`s gain. ORP gain should be much smaller then the pH one. Some commercial solutions let you configure the circuit to make possible to choose it`s application: ORP or pH. The solution I`m using doesn't read all the probe range, but as it's for an aquarium, if I stay between 400mV and 700mV, it would be ok, since far from this point, there would not be any life in the aquarium. Am I wrong?

Well, I got this ORP probe: https://www.aliexpress.com/snapshot/6070876645.html
and this ORP circuit: https://www.dfrobot.com/image/data/SEN0165/OPR meter V1.0 Schematic.pdf

And what about the salinity circuit?

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Hi Jorge
Do you know what U2 is on the schematic you posted the link for please ?

It would be really interesting and useful if you all could enter where you are, next to 'Location' on your user page so that it displays in the window at the left of your posts.

Thanks.

spec

Sorry Spec I didn't realise that I hadn't filled out the complete details as it was quite a few years ago.

markkkk said:

Sorry Spec I didn't realise that I hadn't filled out the complete details as it was quite a few years ago.

Click to expand...

No need to apologist markkk: it is not mandatory on ETO to give your location. It is a bit of a rant with me though because it helps us to give better answers to questions. For example, knowing your location tells us what your mains supply is and also gives an idea of what components you can access.

But the other thing a location gives is a guide to the possible English language skills of the poster. I have also noticed a difference in the outlook from different countries and cultures: Australian, Scandinavian, Canadian, American, Indian, etc.

Taking an example: if you tell an Australian that there is an an error in his circuit he his liable to respond with: "Thanks, too much amber nectar" but at the other extreme, people from some cultures take offence if you point out a mistake in their work.

And, apart from all that, it is just plain interesting, to me any way, to know where people are from.

spec

Thats fine spec. I totally understand. Its pretty hard to get through the aussie thick skin too. I certainly wouldnt be offended with any constructive criticism. None of us know it all thats for sure.

But dont take that as gospel as we still have our fair share of knobs in this country as well but in the main we are all pretty easy going out here in the old convict colony

Yes, I have found your country folk pretty robust and easy going.

By the way, this thread is pretty old so you may not get a reply to your question about the opamp type.

Most of the PH type circuits use either TIL084 or TL074 opamps, but if you want a Rolls Royce PH amplifier use a precision, high impedance opamp, for example the Texas Instruments OPA192 family or the related, cheaper but slightly less accurate, OPA197 family. There are many other precision opamps that would be suitable.

Also, you really need to embody a low pass filter into the PH amplifier so that noise etc is rejected.

In addition metal oxide or metal film resistors and low leakage capacitors should be used.

I have some domestic duties to perform at the moment, but I will see if I can post a circuit later if you would like.

spec

That would be good thanks spec. I have to design a PH and ORP sensor. It is all driven back to a micro to be used for autodosing of pools. I have been looking at a lot of circuits and have come up with high impedance amps are necessary also galvanic isolation. The probes we will use are a all in one PH and ORP with the ORP being gold electrode as these are more stable and as we are using it in electrochlorination you can not use the silver for ORP. The biggest issue is to keep everything calibrated but at a reasonable interval not every week. INA116 are commonly used also. The circuit I have put here I found particularly interesting

The INA116, as you probably know, is a precision instrumentation amplifier (IA). The benefit of an IA is that it rejects common mode interference signals, but not noise.

So for example, suppose the sensor were near a mains transformer, a 50Hz signal may be induced into the two leads from the sensor but as both 50Hz interference signals would be the same the IA would cancel them out. You can either buy a ready made IA or make your own from a precision opamp and four precision resistors

As an aside, here is a link to a Texas Instruments application report: https://www.ti.com/lit/an/snoa529a/snoa529a.pdf

And the data sheet for the LMP7721 precision ultra low input bias current opamp: https://www.ti.com/lit/ds/symlink/lmp7721.pdf

And precision voltage reference: https://www.ti.com/lit/ds/symlink/lm4140.pdf

For those, like me, who are wondering, here is a description of what ORP is all about:
spec

Here is a simple design for a PH sensor amplifier (but I would make both the opamps OPA192), along with a clear explanation of PH meters. https://www.sparkyswidgets.com/portfolio-item/ph-probe-interface/

spec

DATA SHEET
https://www.ti.com/lit/ds/symlink/opa192.pdf

Hi Spec

Thats great info thanks for that I will review all of it. What I have to design will integrate into a existing product we make at my work and also a totally new piece of gear with other purposes as well. I had a meeting this week with a probe manufacturer here in Brisbane. They are one of the biggest world wide manufacturers of probes for all sorts of chemical detection. The original and most popular ORP probes are platinium and mostly used for a liquid dosed pool but these are no good for use in electro chlorination as they get poisoned by the cyanuric acid in the pool water and affected by H2 generation from the chlorinator. They do make a gold version as well. The gold ones do not have this issue and the probes do not need the same cleaning or recalibrating anywhere near as much. There are some issues though using the gold probes but in the main no where near the same as with the platinum ones. The guys I spoke to in this meeting were really smart dudes. They are chemists and dont have any "hardware" type of experience they leave that up to others but it was really good to talk to people who really know their stuff. Still though I have to come up with something that works well and is reliable in the hardware...luckily I dont write the software...I wish I could though. Hardware has never really been a issue for me but the software I just cant seem to get my head around it. I can do simple stuff but not the complex stuff. My brain just doesnt seem to want to work that way

Mark

Hi Mark,

Interesting project. You are obviously designing some professional equipment, rather than hobby, so I think you would be going for highly accurate hardware with low pass filtering and common mode rejection. As the probe readings are temperature dependent I think you would also need to take the temperature of the liquid into account.

spec

Hi Spec
Yes it is a piece of equipment we manufacture at our company that is sold in the aussie market and also in some places in Europe and the USA. The temperature compensation is already done as I have a temp sensor embedded into the epoxy in the electrode. We can actually take a very accurate salt measurement in PPM and it is temperature compensated which is of course vital for the accurate readings so that temperature will be used as well for these measurements.

I not only do electronics for work but also in my own time as one of my hobbies. I ran my own radio comms company for 30 years doing sales and service on radios and satellite telephones. Designed a radio to satellite phone interface for law enforcement here. Also I love CNC stuff so do plenty of electronics for my CNC machine here and also built andfly my own 2 seat aircraft which I am always making bits and pieces up for that as well. Currently worikng on a new intercom for aircraft that will accept all sorts of external radio/telephones so that it can be used for tx and rx via the headsets while you are flying...I am a ham radio guy as well so go "aeronautical mobile" . The intercom also has audio filtering for the mic input as some aircraft can be very loud and a lot of guys have engine audio noise issues and no one can hear them over the noise of the engine especially on trike style aircraft where the engine is directly behind their head. So always doing something with electronics here be it for work or pleasure

Hi Mark,

Wow, you have a lot going on and obviously are into electronics in a big way. Building your own aircraft is no mean task.

spec