Digital 100mA meter reads 1.3mA even tho Laser PSU disabled

[ronguerrero]

Hi,

I have completed installation of the DK40 upgrade kit, but I have not connected WP to a water sensor yet. WP is open. For now I just want to test the rest of the system - DSP display, steppers, limit switches, digital current meter etc. I have connected the digital 100mA meter between the negative of the laser tube to the negative of the Laser PSU. When I power up the system, the digital current meter reads 1.2mA. I thought it would be 0mA if the Laser PSU is disabled? Is this normal?

Note - I have tested the meter with green and blue wires (the wires measuring the current) disconnected, the meter correctly shows 0mA.

Thanks,

[natsterrr]

Hi,

I have completed installation of the DK40 upgrade kit, but I have not connected WP to a water sensor yet. WP is open. For now I just want to test the rest of the system - DSP display, steppers, limit switches, digital current meter etc. I have connected the digital 100mA meter between the negative of the laser tube to the negative of the Laser PSU. When I power up the system, the digital current meter reads 1.2mA. I thought it would be 0mA if the Laser PSU is disabled? Is this normal?

Note - I have tested the meter with green and blue wires (the wires measuring the current) disconnected, the meter correctly shows 0mA.

Thanks,

I've had a similar reading too. I think it works properly while the laser is firing however. And after the laser has finished it appears to jump between 0 and 2 mA. I hooked mine up to the +5V from the awc608 control unit. I wasn't sure how I was suppose to hook it up using the little regulated power thing.

[ronguerrero]

Thanks natsterr.

I hooked it up the digital meter the same way as you. I have no need for for the second Laser output on the board, so I used it's +5V.
Even more odd behavior, I disconnected the HV line and I still get a 1.0/1.2 mA reading. I'll try firing up the laser today to see what happens.

[Tech_Marco]

Try avoid using the DSP 5V to power the meter. Noise may feedback to the board from the ground side of the laser tube. You should use an isolated power module to get 5V from the main power supply instead. You may fine tube the meter by making adjustment on a small VR (potentiometer) that mounted at the back of the meter.

Marco

[natsterrr]

Try avoid using the DSP 5V to power the meter. Noise may feedback to the board from the ground side of the laser tube. You should use an isolated power module to get 5V from the main power supply instead. You may fine tube the meter by making adjustment on a small VR (potentiometer) that mounted at the back of the meter.

Marco

Can you show the best way to hook it up using the little power supply module in the kit? I haven't been able to find any instructions on that part.

By 'main power supply', do you mean 240v? Also, I'm not sure which are the input pins and the output pins of the 5v module thing.

[ronguerrero]

The RF2405CS-2W takes a 24 DC voltage input and spits out DC 5V - hence 2405 in its name.
In our case, Marco is probably referring to the 24V power supply. I was lazy to hook it up, but it guess I really should.
You can use this link as a guide on how to wire it:

viewtopic.php?f=14&t=187

On a side note - my laser tube was busted which I think could have been related to the incorrect readings. Of course I didn't know it was busted until I got really nasty arcing.
I replaced the tube, and now I get around 0.7 mA with the laser off. I'll hook up the 2405 and see what happens.

Update - connected the current meter to the 2405 and the current meter is now reading 0 with the laser off as expected. Thanks!

[natsterrr]

Did you use a shunt? I don't really know what this is.

If I hook the 24v into the little module and then into the ammeter, it should all work ok? (Using the pins as it shows in that link).

[ronguerrero]

The digital meter that comes with the DSP upgrade kit has a built-in shunt.

http://www.lightobject.com/3-digit-Mini ... -P457.aspx

Re: What a Shunt is

http://en.wikipedia.org/wiki/Shunt_(ele ... _measuring

So here the shunt is just a resistor. The meter calculates amperage by measuring the voltage drop across the shunt and divides that by the shunt's resistance.
Introducing a shunt allows the meter to read currents (esp large) without damaging the meter.

[ivantandy]

Based on the the mock setup and pwr source tech photos for the 100mA meter the reference states the meter requires a shunt... I set up my meter with the iso and an interpretation of the wiring based on the photos... likely incorrect since the LED does not light at power on... that said I've yet to identify a suitable power source for my meter since it is a 24V05v ... what do I connect to on the 24V V+ and COM?? my K40 laser PSU has a discrete 5V - have some folks used this as a direct power for the meter? And what about the shunt?- my understanding is the shunt is connected to the cathode (blue in most K40 cases) and the PSU neg (also a blue) across the shunt with the +/- inputs connected from the minor inside connectors. I am unable to power the meter at all in this configuration= where does the meter get its power? 12V 24v or 5V or otherwise. Does one ground it to the PSU or the 24V or the chassis as in the original analog configuration? I connected the cathode wire to the meter's positive = no power; cathode to the shunt is the same result... thus i suspect a separate outside 5V power source is required. As someone who isn't electronic I don't see the missing link described as load in the photo ya sure that's the Voltage source to be measured but how is it that the meter is also powered? The shunt seems a hedge against feedback... comments welcome solutions encouraged.. thnx

dscvrd in forum that simple drop w/out isolation does not work... see pic works w 2405cs OK