Converting Specific Gravity to Milli-Siemens Conductivity

Your Phosphoric acid supplier would be my first contact, followed a close second by the probe manufacturer.

Both would probably have conversion tables for this.

Also, if you are "calibrating" as opposed to "verifying" the probe, then you will need multiple samples across the probe range. Thus you will also need to know the conductivity for those other samples (Even if you prepare them yourself with distilled water).

We do not use that acid, so I cannot provide diract support.

thank you for responding.

when calibrating with the two samples that my supervisor provided earlier today.

the probes appear to be reading to high. not adding enough acid.

i mentioned the results to the operator and he disagreed. in his opinion we are adding to much acid compared to the probe reading.

its near quitting time for me, i will approach this again when i return friday evening.

i will ask for our suppliers name and phone number, thats a great idea. they probably have the best information for that product.

thank you!

using known samples was key in finally convincing the operators and supervisors that the probe is out of cal.

we were able to find the conversion information

1.154 specific gravity = 15% concentration = 92 milli siemens

1.275 specific gravity = 30% conentration = 181 milli siemens

the probe was reading to high, instead of maintaining a 30% concentration in the phosphoric acid tank it was actually operating at 15%.

thanks for the helpful information from all of you. : - )

very nice to have a website that i turn too for advice.

It's in here....

Do bear in mind that conductivity is influenced by temperature, more so than specific gravity.

Ok, if you are attempting to "calibrate" your meter you will need to purchase a certified conductivity standard in the range you are testing in.

Otherwise you are just getting two meters to agree to a reading that may or may not be accurate.

We do monthly verifications of our meters but send them out yearly for professional, traceable, ISO certified calibration.

I bet if you also google chemical test kits for acid strength, you can find a titration kit, that will be even more precise and certainly more accurate. At least use that as a final verification of what you are putting out there. Most modern conductivity instruments have temperature compensation, just make sure that is working, and that any sample cooling is also working or that the tank temperature is well controlled.

Another test that could be useful:

(1) Dilute the sample with distilled (de-ionized, demineralized) water to a concentration range of 20-30 mg/L as phosphate. (to dilute from 30% to 30 ppm requires a dilution of 10,000:1, so you would have to make this a two-step process of diluting accurately and precisely 100:1 twice)

(2) use a colorimetric phosphate test (molybdovanadate reagent is recommended in the test range) to read the diluted sample.

Thank you, i will share this information with my supervisors and coworkers. : - )

i appreciate your help.