Dissolved Oxygen Meter Accuracy?

[sjohns4]

We've got fairly new brand X on-line DO monitors at a wastewater treatment facility. We've got a new brand Y hand held DO monitor at the same plant. The two never read the same, off from 0.5 to 1.0 mg/l. You can calibrate both to a zero solution, but brand X has no other calibration. Our handheld, brand Y, can also calibrate at a known concentration, so I'm wondering if we may have a calibration issue?

Would you expect a hand held unit to read the same as an on-line monitor?

I'm trying to figure out how to test them both to determine which one is right.

Any thoughts or suggustions?

Mike

 

[SteveWag]

I have always considered that the DO measurement is +/- 1mg/L. I would be very surprised if any two meters were closer than that, especially if two different manufacturers or techniques are used. I have never found any of the in-process meters that will live up to the salesman’s claims. ORP does much better in an on-line process situation (in my experience).
Steve

 

[bimr]

Dissolved oxygen is not measured directly with a dissolved oxygen meter. An electrical current is actually measured, which is proportional to the dissolved oxygen concentration. The measurement may be affected by various environmental factors such as salts, temperature, flow, age of DO meter, pressure, etc.

Different manufacturers make use of various technologies in their meters. You can't expect different DO meter techologies to function the same because the meters may be affected differently by the environmental factors. Also, the meters are only accurate at best to +/- 0.3 mg/l.

Consult the application specialist with the meter manufacturer for best results.