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PostPosted: Fri Oct 10, 2014 5:19 pm 
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meppso wrote:
I was informed that Carlisle photocells used to be calibrated to switch on at 55 Lux, then they changed to 70lux. In the early 2000s the Lux level went back to 55 and now it's at 35 Lux!


I recall that whilst PECs were available in a variety of standard switching ratios, in the 1990s when I was really into collecting streetlighting, it seemed that every thermal PEC was 70 lux, presumably because the majority of lighting was still SOX and demanded a longer run-up time.

The NEMA sockets from this period continued to have a datum mark and the word "NORTH" stamped on the top stemming from the earlier requirement to have correct cell orientation in relation to the lantern, especially when used in retro-fit installations to replace the original timeswitches.

Presumably in those early days, operatives would also be trained to re-orientate the socket on brand new NEMA lanterns once they were mounted  on the column.

I think later cells didn't require any sort of setting, i.e the old Zodions with their opal, conical tops and universal LDRs.

On a current streetscene, it does seem that cells switch later than they used to do - in fact I think they switch off sooner too. A couple of local authorities in my area seem to be trialing a replacement for the SS5 electronic PEC. Rather than switch on at dusk and stay on, the cells seem to go "on-off-on-off" with the off period getting progressively shorter as the target Lux level is reached. Switching off in the morning is in the same manner, with the interval "on" decreasing as target Lux level is reached. It might be a faulty batch or a similar reason, but it can't be doing the lamps any good.

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PostPosted: Fri Oct 10, 2014 7:11 pm 
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The cheaper Zodion cells are notorious for "flashing" the lantern at close to the switch point. When you look at what's on the circuit board, its hardly surprising - not a very intelligent circuit with no hysteresis.

Compare with a SELC or Royce Thompson cell which have far more advanced detection circuits.

Thermal cells used to be 1:1 ratio, so for instance 100 Lux on/100 Lux off. Early electronic ones were the same ratio. Many are now 1:0.5, and 35 Lux cells are increasingly being used to "trim" down the number of "burning hours" of the lamp. Therefore its 35 Lux on but 18.5 Lux off in the morning.

As for the thermals, some seem to have the LDR vertically orientated in the dome but RT ones had them slanted on their side in a sort of pocket. This may have been the reason for the NORTH orientation - you wouldn't want the LDR facing the setting sun as this would delay the switching time.

Of course there were also the Cadmium sulphide detectors used with P42/ 2part cells. Calibration of the detector was done by scratching away some of the CdS surface prior to it being enclosed in the dome and rubber grommet.

Oh how technology has moved on!


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PostPosted: Sat Oct 11, 2014 9:36 pm 
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The method of decreasing your burning hours by altering switching ratios (trimming) is all the rage these days. Plymouth's standard is 35:18 now and indeed the Highways Agency have used 20:20 SELC cells too. I'd be interested to see a run of 180w SOX lamps on 20:20 cells. It'd be black and still on red warm-up  :lol:


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PostPosted: Wed Nov 12, 2014 5:44 pm 
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Part night operation of lighting (switching off between midnight and 0530 GMT) is becoming more common.

The part-night function can be within the (electronic) ballast or the photocell.

Both part-night NEMA photocells and minicells are available.

The Lucy Zodion minicell version is the SS19.

Image

The NEMA is the SS9, which I believe is what is used in my village.

Like the majority of photocells it comes with a clear dome.

Coloured domes such as green, blue and orange have been used in the past on all night cells as date of manufacture indication.

However today I received a SS9 part night cell with a blue dome.

Image

I suspect SS9DLS refers to Day Light Saving. However the clear domed SS9 in my collection is just marked SS9 - although it is 6 months newer.


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PostPosted: Sat Nov 15, 2014 11:31 pm 
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Hi All,

Following on from the part night Zodion sensors, in certain places Cumbria County Council used these, Zodion SS59s which were the two part part night version of the sensor. (a bit of a tongue twister lol)

Regards,

Andrew.


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PostPosted: Sat Nov 15, 2014 11:38 pm 
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Hi,

In Cumbria Zodion cells are now the main one part choice. Up here the colour of the cell indicates the Lux level the cell is set at. Blue = 55 Lux, Green = 35 Lux.

Regards,

Andrew.


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PostPosted: Wed Jan 21, 2015 10:48 pm 
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Hi all,

I have just acquired this Horstmann photocell controller, it was manufactured in 1982 making it 33 years old this year. It is a T26 thermal controller. I found a very useful scan on Mike Barford's website detailing this controller. It appears to be a 1: 1.5 switching ratio. I found this unusual for Carlisle as all the other controllers I have are 1: 0.5 switching ratio.

Regards,

Andrew.


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PostPosted: Fri Jan 30, 2015 12:01 am 
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When photocells were introduced they were all thermal.

In thermal cells the switching action is by means of a bi-metallic strip, the nature of which in itself determines that the Lux level at switch off is 50% higher than at switch on - hence the 1:1.5 ratio, and lanterns turning off in broad daylight.

Photocells on sale to this day to the DIY market are in the main thermal with the same positive switching ratio - cheap photocells not necessarily sold at a cheap price!

When electronics entered the equation, it was possible to produce cells with a negative ratio - usually 1:0.5 - resulting in ambient Lux levels (after run up time) being approximately equal at switch on and switch off.

Now with the instant light of LED, and the relentless drive to save energy, the popular choice has become a switch on level of 35 Lux, and whilst logically the switch off level would be the same, because we have become used to negative ratio 1:0.5 cells, a switch off level of 18 Lux.


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PostPosted: Fri Apr 17, 2015 8:47 pm 
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Hi all,

Hope everyone is well?

I have been testing a few P42s and T20s and a few of each don't work. Having looked inside them I have spotted the common cause of failure is the leaded end of the heater becoming detached.  

I think I can get them repaired by a local engineer who can either braise or silver solder them back on.

Has anyone repaired one of these or know where to get a new heater? They appear to have been made by Diamond H controls.

Regards,

Andrew.


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PostPosted: Sat Apr 18, 2015 4:36 am 
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A detached heater element from the bi-metallic strip is a common failure mechanism for thermal cells.

Originally the ceramic heater plate was riveted to the strip. This was very reliable although occasionally the lead wires would come unsoldered - they could easily be soldered back on.

Another method often used by Royce Thompson was to hold the heater on with a small clip.

Zodion used heatshrink sleeving to hold the heater in place. A cheap and nasty approach.  Unfortunately over time the sleeving becomes brittle, splits and then the heater element falls off resulting in a dayburning cell.

They can be repaired using new heatshrink, but I also wrap a few turns of fine insulated enameled wire (the type used in small dc motors) over the top of the heatshrink and tie the turns off.

Fiddly, but the wire being insulation won't short circuit the heater - remember the bi-metallic strip is at ac mains potential, and if the heatshrink splits again, the heater will still be held in place.


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