conductivity variations?

[laurentm]

What is the typical variation in conductivity readings?

My conductivity (as measured by the probe) varies from 52.3 to 52.9. I don't think I have any interferences from the other electrical equipment (I don't see any correlation between the conductivity changes and timer events).

The only thing I could think of, is a slight difference in temperature between the sample collection cup where the conductivity probe is sitting and the sump area where the temperature probe is sitting. There might be a .5degF variation at most (with 2%/degC compensation that would be .6% diff max, right?).

Do you have any idea what else could be affecting conductivity readings (assuming constant salinity)?

 

[clp]

A .5F temperature change would cause the reading to change by .3. The rest of the change is probably from:
- temperture change is greater than .5F
- the temperature compensation value is off slightly
- electrical noise

Curt

 

[laurentm]

<a href=showthread.php?s=&postid=7075240#post7075240 target=_blank>Originally posted</a> by clp
A .5F temperature change would cause the reading to change by .3. The rest of the change is probably from:
- temperture change is greater than .5F

could be but I measured .5F at max variation.

- the temperature compensation value is off slightly

I have it set at 2.1%

- electrical noise

I have the probe cables running together so I should also see some variations for at least the pH probe (very high impedance, right?).

In your setup, do you see such variations or are your readings stable?

Thank you so much for your help Curt.

 

[clp]

If interference from noise exists it does not usually affect all the probes the same. The impedance of the probes, characteristic frequency of the probe, type of of noise, etc. determine whether a particular probes picks up the interference. In the lab here the cond. probe varies by about +- 0.1 unit.

Curt