Failure of Salinity Measurement in Profilux 4

[otimer]

Hello,
I have been running a complete set of profilux 4 since 2.5 years ago.
The temp., orp and pH readings have been very accurate comparing with those with industrial instruments.
I have had some difficulties with salinity measurement from the begining due to electrcal noise resulting unstable readings.
I tried to segregate the cable, adding toroidal ferrite cores etc. It was somting improved, but not so perfect.

Recently, the readings had step changed within couple of ten seconds, several ten minutes or couple of days like,
0.1, 30.5, 0.5, 28.5, 34.0, 28.2 ppt whille greisinger GMH3451 reads very stable 33.9~34.0 ppt.
Finally it stopped at 0.1 ppt all the way long.
I tried to clean the prove with vinigar and citric acid, but the result dosen't change.
As far as I understand, probes at their end of life, usually their output go down gradually and eventually go out of calibration range.
Is this also a phnomenon one of those shown at the end of life of conductivity probes?
I'm concerned about the input circitary of Profilux 4.
Before I buy an expensive new probe, I'd like to check the reason, probe or circuits in Profilux 4.
However, the Profilux salinity readings are not so essential to me, as actual salinity is very stable and I measure with GMH once a week.
Any help would be appreciated.

Son

[Vinny]

Hi,

You can test the probe by taking a cup of tank water and sitting the probe in it for an hour or so. Observe the values shown in the ProfiLux. If they are steady, then there is interference in the water or area which is disrupting the sensor's accuracy. You can also verify the accuracy by sitting it in a sample of 50mS calibration fluid. If the results match very closely, the probe is working. At nearly 3 years though, the probe is most likely just due for replacement.

[otimer]

Dear Vinny,
Thanks for your reply.
I did check that way, and again tried to measure the tank water in a cup this afternoon.
But the reading has not changed.
I should judge the probe has ran out his lifespan.
Thanks again.

Son

[otimer]

This failure has been cleared by replacing the probe with new one.
Thanks~!

Son