But what's a few orders of magnitude when high voltage is concerned??? ;)
(I've been focusing to much on the mV output)
And one other thing, esp. for newbies--the electronic boards have
somewhat diagnostic LED's on them. Look at them, take a picture, when
things are working--both with source and/or high voltage on and off.
That can help you troubleshoot--and sometimes isolate problems to the
controller board for a given lens. (no, it won't tell you if a lead
came off). For older systems, look to see if there is a rechargeable
battery being used as a constant voltage source--and check the voltage
(with the high voltage off!!!).
There is also something to be said for having a sister system so you can
swap parts (alas, I haven't seen any 2 for 1 President's Day specials).
But check with the company to make sure the two systems' boards are
indeed interchangeable. IF something like one of the controller chips
fail, swapping out the bus board will tell you that's an issue.
Also, the PC's can fail, and that shows up in weird ways. Just
switching slots for the control card may fix some issues. Also PC power
supplies age, which can lead to a failure to communicate...
On 1/12/2016 6:58 PM, Peter Stow wrote:
> Dear Gerry,
> Good to see you last week. I think the autocorrect is putting an "m"
> in front of everything. The maximum filament current should be 5A
> (amps) and the high voltage 3000 V (volts).
> On 12/01/2016 10:33 AM, gerard olack wrote:
>> HI Andy--
>> 1. The heating current is 5mA, the emission sits on top of that. It is
>> current limited--so the bad batch of filaments that went out a while ago
>> looked like they might have been too thick and carried too much
>> current--so the over all current limit was hit before you got good
>> emission. If the leads are (close to) touching in the source, then the
>> current bleeds thru that way. Probably not a problem for you Also I
>> remember hearing about a bad batch of source heaters--they would leave a
>> deposit on the insulators--so a small leak to ground at voltage.
>> 2. Our set up has the HV showing in Volts--and it goes from 0 to 3000
>> mV. So it should go all the way to 0 mV. You can even check for
>> problem with voltages at say 1000 mV? Everything should float on the
>> hV, which, at least according to the readbacks, bounces around a
>> little. It may also float a little away from your ground--depending on
>> what you're using for ground--but that shouldn't be much.
>> good luck
>> On 1/12/2016 10:38 AM, Andrew Schauer wrote:
>>> Greetings list,
>>> Two questions:
>>> 1) Does anyone know what the current range THROUGH the filament is
>>> supposed to be? I am not referring to the emission (~ 1.0 mA). We are
>>> having a complete loss of signal and right now it looks like the
>>> current through the filament is not varying as a function of the
>>> potentiometer (physical potentiometer on the face of the instrument).
>>> When I vary the potentiometer I see no variation for most of the
>>> travel and the a sudden drop to zero volts (across a resistor that
>>> escapes me at this moment).
>>> 2) For the Isodat software 2.x on windows xp, if I vary the HV
>>> [steps], from 0 to 3000, what should I expect in terms of real high
>>> voltage variation? For example, if I measure voltage between (yes
>>> using appropriate high voltage probes and caution) ground and "col".
>>> To call out two of you that may be listening (Peter and Christie), we
>>> talked at the clumped conference about this loss of signal issue. The
>>> source connections are all sound (I vented it and checked each
>>> connection which were all very solid). I also measured no connection
>>> between any feedthrough and another (apart from the 0.2 ohms for the
>>> filament). I also observe expected magnet strength when I hold a metal
>>> object near the magnet during hysteresis.
>>> Thank you.
>>> Andrew Schauer
>>> [log in to unmask] <mailto:[log in to unmask]>