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#11
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Testing trigger voltage
AVO, they'er Test meters (Amps Voltage Ohms) but we knew them as the
'bees knees' of testmeters - built like a tank and normally used a moving coil meter as opposed to a digital read out. Digital meters usually have an input around 10 M ohms per volt, meaning that if you are measureing 2 volts the circuit will see a 20 M ohm resistor across it's terminals. A moving coil meter could be anywhere from 1k ohm per volt to arounf 100 k ohms per volt, meaning when we measure say two volts an 100K ohm testmeter will represent a 200K resistor across the circuit your testing. The lower the current drawn by a testmeter the more accurate the readiing and modern circuits use very low currents. It's not easy to measure the flash voltage because of the rise time - the moment of applying voltage to trigger the flash and the time it takes for the meter to register the voltage, moving coil or analogue meters as they are known are totally useless, digital meters fare no different although better, so slow not to give any readings that is anywhere near accurate, by the flash has gone the poor ol' meter will still be responding. The correct way is to use an oscilloscope, not only could you measure the voltage you could also measure the 'rise time'. I am curious to know the reason why you need to measure a voltage, it's something that normally isn't done even in a microwave oven it's never necessary to know the magnetron's supply voltage...! Flash tubes normally use a 'trigger transformer', charging a capacitor to around 2,000 V (2kV), the firing circuit which could be transistors or thyristors. A little off topic .... Davy |
#13
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Testing trigger voltage
"Allan" writes:
Yes, DVM is Digital Volt Meter. AVO is the trade name of a British company (AVO Megger) that makes high quality multimeters and other lab grade test equipment - considered by many as the multimeter of choice. Never heard of them in North America, so AVO probably means nothing to a lot of readers. It doesn't matter what specific brand of DVM you use, but it should be something with at least 10 megohm input impedance to measure the trigger voltage accurately. Any *good* lab or portable DVM should meet this, though I wouldn't assume it was true of a cheap meter bought from an auto store. Dave |
#14
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Testing trigger voltage
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#15
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Testing trigger voltage
The voltage drop across the trigger is NOT measured during the brief
interval that the flash is being discharged. AMPERAGE would be measured then. The voltage is continuously present -- for MORE than enough time to be measured by even the SLOWEST response meter. High-voltage damage will occur to a camera's circuit as soon as it is applied, whether the flash is triggered or not. Voltmeters are all high impedance. Although a HIGHER high impedance will theoretically draw less power, this application does NOT require it. It makes no difference whether the meter shows 185 or 300 volts -- if it is over 6 volts, it is too much. |
#16
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Testing trigger voltage
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#17
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Testing trigger voltage
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#18
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Testing trigger voltage
In article , Roy Smith
writes In article , "Allan" wrote: I was just doing this before I looked at these posts. One of the other posters and the site mentioned both suggest a DVM to measure the voltage and that was my first choice. However, I have discovered a problem. The problem is the readings on the DVM's (two of them) do not agree with my AVO. For those who know, AVO's do not lie. Both DVM's measure 94 volts on my Vivitar 283, while the AVO says 212 volts. I'm assuming DVM is Digital Volt Meter, but what's an AVO? Amp volt Ohm. -- Ian G8ILZ |
#19
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Testing trigger voltage
In article , Fred McKenzie
writes It must be Analog Volt Ohmmeter, which explaines the reference to 20K Ohms per volt. Nah, it predates digital meters by so much that analogue was the only sort and there was no distinction to make. -- Ian G8ILZ |
#20
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Testing trigger voltage
In article , Davy
writes A moving coil meter could be anywhere from 1k ohm per volt to arounf 100 k ohms per volt, meaning when we measure say two volts an 100K ohm testmeter will represent a 200K resistor across the circuit your testing. The Avo 8 & 9 are 20k ohm / volt, which means that on the 1000 V range it would be higher than the 10M ohm of a typical DVM. The lower the current drawn by a testmeter the more accurate the readiing and modern circuits use very low currents. Usually, I once had inaccurate readings due to contamination acting as an electrolyte and causing an offset voltage which collapsed when a lower impedance meter was used. -- Ian G8ILZ |
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