Using A Multimeter

[achris]

Re: Using A Multimeter

Hi all,

This is the basic circuit of a DVA. All 3 components are available at any electronics shop and shouldn't cost more than about $1.

Theory of operation.

The signal from the stator, triggers and switchbox are, essentially AC in nature. The the signal is rectified by the diode and then stored in the capacitor. This is what the multimeter will measure. The resistor is a 'bleed-off', so the charge in the capacitor isn't held for too long, about 3 seconds.

When you buy the components, just make sure the capacitor is a 'green cap' or polyester and rated at 1000v. The 1N4007 diode is rated at 1000v.

Chris............

 

[ThumbPkr]

Re: Using A Multimeter

Looks like an old "RF" probe.Have to look in my old ARRL handbook to compare circuits)
I imagine an RF probe would have a trimmer capacitor to calibrate it though.I have built them in the past for my scopes.Ron G

 

[jtexas]

Re: Using A Multimeter

Capacitors don't discharge AC, so isn't powerpack output DC? that being the case, is the diode really necessary?

Trigger output is only half a volt, which is overwhelmed by the voltage drop across the diode. This circuit for measuring very low voltages using a dual op-amp was recommended on an electronics forum. I haven't tried it and don't know enough about electronics to evaluate it.

 

[achris]

Re: Using A Multimeter

This is what's known as a 'virtual diode'. The only problem with this is that it needs a dual power source for the op amps. +/-15 volts typically.

The trigger voltages are around 3 volts, so with the forward bias voltage drop of the diode, although is significant, is not too much.

The switchbox output is not AC, true. But it is not a pure enough DC to use the DC setting on the meter. The diode will stop the charge stored in the capacitor being bleed back into the circuit in the switchbox.

Chris..........

 

[jtexas]

Re: Using A Multimeter

looking at the CDI chart for OMC, I see .5V for trigger?

http://cdielectronics.com/LinkClick.aspx?fileticket=iQIrxBxUGx0=&tabid=55&mid=383

thanks!!

 

[achris]

Re: Using A Multimeter

ok.. I accept that... I usually only work on Mercs... Trigger voltage is around 2.5V min.

Cheers,

Chris........