Magnetic Level Probe Mk2

[Penri]

Update design and implementation document for the Mk2 probe attached

[Penri]

To keep the forum up to date with progress a further 4 probes have been assembled and tested (they work on the stand alone test rig).

These probes will be trialled with the Hanham Room RPi assembly to ensure they operate correctly with the RPi interfaces before installation.

[Penri]

Investigation into potential problems with Sump probe:

External visual inspection - Probe taken from sump
Probe and connecting cable fairly dirty but otherwise looked sound.

Internal visual inspection - Probe taken from sump
Probe electronics looked like new, no visible sign of any water staining or corrosion. One of the joints in the 3D printed support sections gave way on removal but wiring held probe together, sections re-glued.
No water in probe tube.

Electrical inspection on test rig - Probe taken from sump
On power up probe appeared normal and each Hall effect switch responded correctly when a magnet was placed near it.
I noted that one meter needle, the one associated with x00 looked higher than the others so conducted some further tests (results in the attached document).
The results in the attached document shows that the x00 channel has a higher chain resistance than the other three channels by around 3k ohms and also the voltage at the probe O/P is higher by around 110mV probably as a consequence of the higher chain resistance (but that needs further investigation).

Electrical inspection on test rig - Spare probe
Tests (summarised in attached document did not show same discrepancy as the Sump Probe so took the decision to swap over the electronic assemblies.

Having completed the testing I re-packaged the probe in the sump probe tube, re-tested it and am currently soak testing it before return to WMT later this week-end / Monday morning.

I will carry out a deeper review of the original sump probe electronic circuit to try to establish the cause of the discrepancy in measured values.

[Penri]

Bench test of Hanham probes 20Feb22.

Blue top probe, the one with the longest flying lead - checked out ok, reading obtained at each 25mm step.

Black top probe, the one with the medium length lead - checked out OK, readings obtained at each 25mm step.

Pink top probe, the one with the shortest lead - flexible 3D printed top had delaminated and would no longer offer any environmental protection so was changed for a Blue top (I only have 2 spare tops one blue the other black) with the word Pink written on it.
Initial investigation revealed that 875mm level was not returning a reading and that all X50 readings were intermittent.
The probe was disassembled and the electronic assembly removed, there was no sign of water ingress and internal components were all clean.
The joint between the top two carrier segments has failed so that was repaired with CA adhesive.
There was no continuity between the 875mm Hall effect switch 0V i/p and the 0V line, there may have been a dry joint when initially manufactured and the failure of the adjacent segment joint (see above) had caused it to come apart. The solder joint was remade and continuity was restored.
With the probe functioning, moving the flying lead/connector caused the X25 and X50 indicators to fluctuate.
The flying connector was disassembled revealing poor solder joints on the Yellow and Violet conductors, these were remade and resoldered.
The probe was then re-tested and checked out ok, readings obtained at each 25mm step.

Testing was repeated on each probe and all checked out ok.

I will repeat the tests tomorrow to ensure all still ok.

[TerryJC]

Penri,

Those results are rather strange. Leaving aside the blue topped probe the other two definitely exhibited reproducible faults that moved when the probes were moved. Did you test through the connector in all three cases? That's the only thing I can think of.

[Penri]

Terry

All the initial and final tests were via the respective flying connectors, I only disassembled what was the pink topped probe.

Given your misgivings I'll take the other two apart to see it there's any viable sign of issues inside.

As I said I'll be re-testing tomorrow, I'll give each a good shaking as part of the activity.


Penri

[TerryJC]

Penri,

I can confirm that all three probes appear to be working as they should; the only problem is that the readings are still incorrect.

I connected everything up and found the same results as I got before Penri tested (and repaired) them. I then measured the voltages at the Terminal Blocks for G2 and G3 (I can't get to G1 when the system is installed). With the Unit Test Software returning 'Not Triggered', I measured:

• 12.07 V DC between TB2 Pins 13 and 14.
• 3.1 V between TB2 Pins 15 and 14.
• 1.5 V between TB2 Pins 16 and 14.
• 3.1 V between TB2 Pins 17 and 14.
• 3.1 V between TB2 Pins 18 and 14.

I got similar results at TB2 Pins 7 to 12 (G2) and at different levels on G3, all while the software is returning 'Not Triggered'. I can't see any logic to this at the moment and it's going to be difficult to work on this hardware until I can get it into my Workshop and out of the IP65 Box. The only thing that I can think of is that for some reason the software is not seeing the dip, even though it is solid enough. I did wonder about noise pickup from my lights in the garage (just the same when off), or some kind of magnetic effect from all the Dexion racking in my garage???

Penri,

Do we have another probe that is not fitted with a round industrial connector? This would make it much easier to test the kit in my Workshop.

I'll transfer this narrative to a new Topic to cover the Lady Hanham SAC diagnosis and repair.

[TerryJC]

I've started the new Topic at viewtopic.php?p=5619#p5619.