Erratic ORP readings

[Submerged]

Hi,

I have 2 Aquacontroller II base units. The same ORP probe (standard), when connected to each of the units reads >100 mV different (410 on base unit 1; 290 on base unit 2). I'm using the same power supply for testing purposes. I have each unit positioned in the same location when I run the test.

The PH probe (also standard) reads 8.3 on base unit 1 and 8.45 on base unit 2. I callibrated the PH probe on both base units.

Thoughts anyone? I'd prefer not to have to buy a separate ORP monitor just to figure out which base unit (if either) is reading accurately.

 

[clp]

Follow the calibration procedure in the manual to calibrate the ORP probe. If you have a serial cable plugged into the controller try unplugging it and see if it effects the readings. If so, then there is a ground loop and you need an isolator (SERIPC9).
Following calibration on the pH probe with the controller in the 'run display' make sure that each reads 7.00 in the 7 solution, and 10 in the 10.00. If so then the controller is properly calibrated and the measurements should be accurate.

Curt

 

[Submerged]

No serial cable plugged into either base unit, but the pH will drop about .1 on base unit two if I raise the ORP probe out of the water. They're not close to each other (roughly 2 feet between probes). Also, I didn't receive any quinhyrdone with the calibration packets...just a bunch of pH 4, 7, and 10. Any idea where I can find some quinhydrone?

The manual says to create a "saturated" solution of Quinhydrone and pH 7.00. How does one do this?

 

[clp]

You can find quinhydrone from a local lab supply store - try lab supplies in the yellow pages.
You keepadding quinhydrone to the pH calibration solution until it no longer dissolves.

Curt

 

[Submerged]

ok- will give that a try. related...should I have pH Comp: ON or OFF? Similarly, should I have Temp Comp: ON or OFF under pH Setup?

Thanks.

 

[clp]

I recommend leaving pH compensation off for the ORP probe as that is the industry standard.
Since the temp. change is so small in a typical reef tank, it is probably best to just leave temp. compensation off on the pH probe too. It is a very small adjustment.

Curt

 

[emelton]

You keep adding quinhydrone to the pH calibration solution until it no longer dissolves.

Curt

OK, you keep adding it but shouldn't there be a certain ratio for an accurate/definitive calibration target number within +/- 3%?

How come Neptune systems cannot give a straight forward answer on how a customer can calibrate their ORP?

Just come up with a calibration solution for the ORP probe like there is for the PH.

 

[clp]

I think we have been giving a straight answer on making the ORP calibration solution. You need to make a saturated solution of pH calibration solution and quinhydrone. So do the following:

- Start with a packet of pH 4.0 solution
- Add quinhydrone until it no dissolved into the solution. If you add too much it doesn't really mater you are just wasting the quinhydrone.
- Use this solution for the 4.0 quinhydrone calibration point.

- Start with a packet of pH 7.0 solution
- Add quinhydrone until it no dissolved into the solution. If you add too much it doesn't really mater you are just wasting the quinhydrone.
- Use this solution for the 7.0 quinhydrone calibration point.

This solution is not premade as it is not stable over time, and wouldn't be a good calibration reference.

Curt

 

[emelton]

What are the target numbers? for both solutions?

 

[clp]

You don't really need to know as this is handled in the controller automatically. The 4.0 quinhydrone solutions is 275 mV, and the 7.0 quinhydrone solution is 90.

Curt

 

[emelton]

Here is the way to write an ORP calibration proceedure:

http://www.automatedaquariums.com/tecorpca.htm

Thank you automated aquariums.

 

[clp]

Maybe I'm just biased, but I think that the procedure in the AquaController manual is straight forward and easy to follow. Perhaps more details on how to make a saturated solution of Quinhydrone could be given, but I thought 'saturated' was self explanatory. Here is the procedure in the Aqua2 manual:

1. Create a saturated solution of Quinhydrone and pH 7.00 calibration solution.
2. Select Setup:ORP Setup:ORP Calibrate from the AquaController
IIââ"šÂ¬Ã¢"žÂ¢s menus.
3. Place the ORP probe into the Quin-7.00 solution. Wait for the
numbers on the bottom of the LCD screen to stop changing. It
does not matter what value is displayed only that it is not
changing. When the display stops changing press the select
button.
4. Create a saturated solution of Quinhydrone and pH 4.00
calibration solution.
5. Place the ORP probe into the Quin-4.00 solution. Wait for the
numbers on the bottom of the LCD screen to stop changing. It
does not matter what value is displayed only that it is not
changing. When the display stops changing press the select
button.
6. The ORP probe is now calibrated.

Curt

 

[kattner]

Here is the way to post a question requesting help:


1. Use the word "please" - this always helps in the initial stage of the conversation.

2. Do not tell people who have responded that they should know you already tried their suggestion. This is not very polite and can abruptly end the help.

3. Never accuse the person trying to help that they are not giving a straight forward answer. This will never get you anywhere.

4. Use the word "thank you" so the person will help you the next time a question comes up.

 

[emelton]

You don't really need to know as this is handled in the controller automatically. The 4.0 quinhydrone solutions is 275 mV, and the 7.0 quinhydrone solution is 90.

Curt

Thank you..

 

[flying-pro]

did mine. I thought the manual was fine.............