Perhaps using cold cathode tubes would be much better then? As far as I know, the whole point of having a hot cathode is to make starting (a whole bunch!) easier -- with a sufficiently high voltage you should be able to 'jump start' the lamp directly, just as is done with neon tubes. (And of course you can use a regular fluorescent tube as a CCFL tube by just not heating the cathode!)
Come to think of it, seeing neon tubes switching on and off every second or so all night long isn't that unusual...
OKAY... Put together a RFQ including and --- How many? what size display? Voltage or current? Provisions for how many ranges? Resolution? Environmental considerations? Operating voltage? Isolation requirements?
Would a Blue white display behind a polarized panel be OKAY? OR Color preferred? LED or?
Send to: snipped-for-privacy@pacbell.net
They will quote in USD. From what you suggest here, Less than $862 USD How much? Fill in the data!
I doubt that, because I have seen a great deal of 4", 6", and even 8" panel meters on the market. In fact, your local repair garage likely has quite a few of these on their diagostic and wheel alignment systems.
"Unlike incandescent or fluorescent lamps, neon tubes can be switched on and off continually, or dimmed, without affecting the lifetime."
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That sounds like it would work.
"There is such a thing as a cold-cathode fluorescent lamp. They resemble "neon" signs, but are generally of slightly greater diameter. They are not too standard nor widely available. They are also typically a bit less efficient than hot-cathode lamps. However, they can be dimmed to any degree without any chance of damaging them or causing any excessive wear. It should also be noted that starting these frequently does not cause any excessive wear. (If excessive current flows during the first half-cycle of operation, a generally insignificant amount of extra wear occurs.)
There are also miniature cold cathode fluorescent lamps, often used for backlighting LCD screens and in image scanners. (LCD screens sometimes use other means of lighting such as a white electroluminescent panel.) Like the large ones, miniature cold cathode fluorescent lamps are dimmable.
Many "neon" signs are actually a variation of cold-cathode fluorescent lamps!
There are dimmable, electrodeless compact fluorescent lamps generally known as induction lamps. These are now available from electrical/lighting supply shops. These use an even different way to get electricity from metal to gas. These lamps work at a very high frequency, which lets current flow capacitively through the glass or use induction to get power from a coil to the mercury vapor discharge. No metal electrodes touch the mercury vapor discharge. These lamps should work at least reasonably well with ordinary light dimmers."
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(This page also has some discussion about heating the filaments with a lower wattage. This might work for flashing as well.)
Not nessesarily. If you use relays in place of old-fashioned starters, keeping them closed will keep the lamp off, and opening them will allow the lamp to start instantly. [Dunno what that does to lamp or ballast lifetimes, but flourescents _can_ switch quickly.]
You can do it like some old scoreboards. Use a piece of thick red Plexiglas. Cut it into strips for each segment, paint the sides black, and drill holes in the back side for small lamps like the old 1847, or the newer automotive side marker bulbs that push in. If you use four or five lamps you can loose a lamp or two and still see the segment.
To clarify. Earlier this year I was looking for industrial wall-mounting digital meters to bolt on top of the machines that could be read at up to about 20m, say from the production office or anywhere on the shop floor, and would indicate the current value of a 0-10V process signal. I had in mind multi-LED seven segment displays. Sure, wheel balancers, car park counters and such, incorporate suitable displays, but they are built in, I can't bolt them to the factory wall or connect them to the process. I was looking for something installable by the resident electrician - a contractors bill for panel building or interfacing would push the cost back into the stratosphere (where accountants can't breathe).
The lamps would work, but not always start reliably, since the off times would vary and the plasma path would cool at different rates. The ballasts would be stressed, being current limited by inductance (assumption - not electronic) but would run at full power all the time, thus reducing or at least not improving life expectancy. If you were displaying data which changed in minutes, the fluorescents would work just fine.... Readable for a great distant.
Actually any florescent can be used as a CCFL by providing much higher starting voltages. Even so called burnt out tubes will light, although at that late in life the output is much lower. The trick is to use them on HVDC. The color changes too, so I haven't seen it done much!
Some years ago, I designed some with 3" displays but we found the marketability to not be all that great. It's one of those things that a lot of people *say* they want but when you go and make one, and figure out how much it costs, many lose interest. There are up to
200mm (8") displays available, but the MOQ $, power required, PCB cost and the housing cost goes up pretty fast at those sizes (with the square of the height). Of course if you're actually into making scoreboards..
The Oregon State Lottery 'dot-matrix' semi-graphical color displays aren't too bad. I'll bet they aren't that expensive given they're found in so many cafes and truck stops. Don't know who makes 'em.
There is no "off" time, the tubes are either "ON" or in "Start" mode, where the current through the filaments in the ends keeps them warm. This is the old-fashioned 'short the ends to start the tubes' paradigm, where the starter is a separate device....
I am pretty sure that what erodes the electrodes is ionic sputtering. This is basically cratering of the cathode by impact of positive ions accelerated by the end-to-end electric field. This process, and electron impacts at the anode, are what keeps the electrodes hot when the heater turns off, but the heavier positive ions do more damage (same energy (= e * electric field * mean free path) but more momentum). I used to know all this stuff in the days of valves (vacuum tubes) but I haven't revisited it for decades. In high school at every opportunity I played with vacuum pumps and electrical discharges.
Of course both the electrodes are alternately cathode and anode when using AC supply, so both wear equally.
So to keep it running you need to supply a reduced heater current during 'off' to maintain the same heat input as the ion flow normally produces. The rate of electrode ablation will certainly be reduced in the absence of plasma current, not increased, so there is no abnormal ageing problem.
If the gas wouldn't conduct straight away then how would the lamp normally start? We heat the electrodes to get electron emission, then apply working voltage and "hey presto" it conducts and lights. With hot electrodes you don't need any HV striking pulse like say a sodium lamp - try it, it fires just like a neon lamp. Inverter driven fluorescents like for caravans don't have any circuit for an HV pulse, they just fizz a bit then get brighter as the electrodes heat up.
The gas doesn't have to be ionised to 'conduct' the electrons, they just ionise it in passing, and while the gas is being ionised, it glows in the UV as the battered atoms recombine and return to ground state. When the current ceases the glow dies pretty instantly on a millisecond timescale, so the excited population must have collapsed in that time. Most of the light decay time ( a few ms) comes from the phosphor - the lower energy (visible light) excitation states are longer lived.
You need a lot more current density for ionisation to make a significant difference to conductivity. Think arc welder.
What we don't get at cold start with any metal-vapour tubes is full vapour pressure, so we don't get full brightness for a while, and presumably a somewhat higher striking voltage. Brightness might be a problem for the
7-segment display. You'd have to keep the tubes in a warmed enclosure to get around it. Or use noble gas (eg neon) tubes like someone said.
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