Pyronix LCD keypad, display acting oddly

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Evening all,
got a keypad display that is acting rather oddly so thought I would check here to see if there is any known problem before I start digging.
The panel is a Pyronics Euro46 with 2 wired keypads, a Euro46 basic one adjacent to the panel for maintenance and a EURO-LCDPZ (the flashier chrome one) by the front door. There is also a zem32 wireless expander on the RS-485 bus.

The problem is that the display on Euro-LCDPZ keypad doesn't just update fairly instantaneously in one goas you would expect, parts of characters update then half a sec later the rest update so if you're flicking through menus lots of bits of characters appear then half a sec and the rest fills in so you can read it. By comparison the other keypad next to the panel updates the display normally.

The odd thing about this is that I set everything up on the bench initially to program it and I don't recall seeing any problem then but it was immediately noticeable on powerup when installed.

Everything actually works fine, no bus errors or other problems, the rs485 bus is cabled in Cat5 and is approx 7m length. It doesnt run parallel to any power cables but crosses one or two. The bus terminations all look ok, there is a 470 ohm resistor terminated both at the keypad and the panel and the cable from this keypad goes through a ferrite core at the panel as per installation manual.

Anyone come across this before?, I am wondering whether noise on the bus could cause this effect as it seemed ok on the bench.
 
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Swap keypads round and see if problem follows

Reckon thats the next move, I will have to take the dodgy keypad off on Monday anyway whilst the wall is re-papered so was just going to stick it on a short cable at the panel in place of the longer bus cable that normally feeds it to see if it behaved differently but swapping will prove the bus cable at the same time if the problem moves with the keypad:D TA!
 
Check for induced A.C. voltage on data bus.
If you have a multimeter, set to AC put one probe on + on data bus and other probe on earth . What is the reading ?
 
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Check for induced A.C. voltage on data bus.
If you have a multimeter, set to AC put one probe on + on data bus and other probe on earth . What is the reading ?

Thats the plan if its not just a keypad fault. The bus cable runs up an old, spare steel conduit in the wall (1920's bungalow) its got an old earth terminal on one end but not checked it for continuity as it only has the bus cable and a cat5e cable to link router to poe switch (cameras next weeks little job). Hopefully will be able to check for any induced voltage in the cable tomorrow, although i might swap keypads first and see if problem remains with the keypad or the bus cable.
What I am not familiar with is whether induced noise/ac on the bus cable is likely to cause the sort of effect I am seeing, a rather slow and fragmentary update of the display. Im guessing that the keypad does not have any significant processing capacity and all the display data is held on the panel and rewritten to kpd when anything changes which made me think it might be a bus issue...hopefully will find out tomorrow.
 
I had a chance to look at it today, swapped the keypads and the problem stays in the same location, the hall where the known "good" keypad also now updates rather hesitantly, so keypad is OK

With the panel powered down and keypad and terminator disconnected (hall) I measured on A/C volts back towards the panel:
D1 to D2 twisted pair fluctuated between 0.00 and 0.02mv
D3 to D4 twisted pair fluctuated between 0.02 and 0.05mv
however measuring between the pairs 1.e. D1 to D4 i got 1.5mv, similarly between D2 and D3, d2 and D4 etc.

I checked whether the conduit is grounded and its not but when I tried earthing it measured voltages above increased slightly:(

I mentioned in an earlier post the bus cable runs down inside the wall in an old steel conduit, nothing else in it except a low voltage bell wire and I isolated that to prove its not causing the problem. I pulled a second cat5 cable into the conduit at the same time as the bus cable which I intend to use to link the router with a POE switch in another room, solid floors so everything has to go via roof space. This cable is unterminated and currently just chucked in the roof space..and on the floor under the keypad. I looked for induced voltages in that and was getting 175mv across the pairs although you can get that sort of reading just dangling the meter leads near power cables so the numbers probably dont mean too much in this case.

Anyway, decided to ground all conductors at one end of the spare cable sharing the conduit with the bus cable and the display update improved a little:). As bus cable has 4 twisted pairs, only 2 of which are in use I also tried grounded the spare conductors at the panel but that didn,t make any difference:(.

It would appear that the hesitant display updating is probably due to mains induced noise and possibly the only way of improving things further is to pull out the cat5 and replace it with shielded cable. I have to take keypad off again tomorrow whilst wall decorated so I might just stick keypad on a 7m length of the same cat5 cable, well away from any mains interference and see if it behaves ok just to see if its normal behaviour for pyronix keypads to update their displays slowly when used remotely (aware I could be looking at something which is just normal behaviour.)
Any observations or magic solutions most welcome!
 
Have you tried it with normal alarm cable and not cat 5 ?
No I haven't mainly because a twisted pair cable should in theory have better noise rejection than a straight alarm cable. I noticed in Pyronix installation manual it says you can run an rs485 bus for upto 1000m in 6 core alarm cable, doubling up D1 & D2 or the same distance in twisted pair cable... it also says use screened cable when running near 230v mains power wiring:(, its not far from mains cabling (20cm away for d istance of 2.2m and both mains cable and bus cable in separate steel conduits)but must admit I thought being in seperate steel conduits would shield things enough
 
Leave control panel switched on and take reading between data bus + and earth with meter set on A/C what is reading ?
Good idea to run temporary cable from control to keypad postion to see if same issue,.
 
Leave control panel switched on and take reading between data bus + and earth with meter set on A/C what is reading ?
Good idea to run temporary cable from control to keypad postion to see if same issue,.
as suggested, readings to eth (mains eth) from bus cable
D1 0.003V to 0.5V with periods upto 5.4V
D2 same as D1
D3 1.4V with periods several seconds of 4.4V
D4 same as D3
from an analogue indicator on my meter you can see the voltages randomly bouncing up and down so its difficult to see exactly whats actually going on, could be mains noise or data stream. If you can say what I should (or should not) be seeing then I can get the scope out and see whats happening. I'm going to run a temp cable in a bit to see if problem goes away....will retest bus voltages as comparison
 
ran a temp cable for keypad in cat5 and also tried it with normal alarm cable, just run across floor nowhere near mains cables. it seems to be working normally
rechecked AC voltages to earth as I did earlier on original cable and result quite a bit different

cat5 temp cable
D1 4.578-4.601 variance of 0.023v
D2 4.575-4.590 variance of 0.015v
D3 4.712-4.729 variance of 0.017v
D4 4.724-4.755 variance of 0.031v

retested using std alarm cable
D1 4.526-4.530v variance of 0.024v
D2 4.513-4.557v variation of 0.044
D3 4..663-4.720v variance of 0.057v
D4 4.670-4.710v variance of 0.040v

in both these last cases a gradual slight rise and fall in the AC voltage measured, in all 3 cases the keypad was in engineer mode. Question!, if around 4.6v ac is the normal steady state for the rs485 bus, what was I seeing in earlier post where the power pair d1,d2 were showing less than 0.5vac for several seconds then upto 5v for a few secs then back down again and the data pair d3,d4 doing a similar thing, would this be the bus restarting due to errors perhaps?
 
Any a.c. induced voltage 1.2v or greater I would fit a act 1313 filter.
Running a temp cable has possibly answered the question and keypad is not faulty.
 
Any a.c. induced voltage 1.2v or greater I would fit a act 1313 filter.
Running a temp cable has possibly answered the question and keypad is not faulty.
Agreed the keypad does not appear to be faulty.
Must admit I was a bit puzzled by the voltage measurements, the first set when the keypad was connected through the installed cable were all over the place, 0.002v one second then 4.6v for a bit then down again whereas measured on the temp cable there was a steady 4.5v ac all the time. I had a look at the temporary bus cable this evening with an oscilloscope. With respect to either D1- or D2+ the data pair is clean with trains of pulses of 2.5v at around 2us although the whole cable has 4.5v ac on it. Looked a bit further and the DC supply at the panel, as I guess you were suggesting, also has 4.5vac superimposed on it.....guess that explains the steady AC voltage I was seeing on the temp cable. On its own it didn't affect the keypad as the AC on both legs of the data pair was in phase and the pulses are equal and opposite on each leg so keypad just saw clean data pulses.

I am guessing that the induced AC will be feeding back from all the wired sensors around the house I will follow your advice and get an act1313 filter and fit that first before looking again at the cable run which seems to be causing the problem. It would be nice if it cured that too but I still havent worked out why I saw an ac voltage for a while, then virtually nothing for a few seconds then ac back again for a few secs. Ill see what it does with a filter in place, thanks.
 
Just an update, fitted an ACT1313 filter as advised by Handymanjo and induced AC dropped from 4.5v to 0.3v, excellent result and AC voltage readings to eth at the keypad no longer are bouncing around as before. Keypad display is much better now so thanks for the advice.
 

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