Laserscope Startup Sequence

[mixedgas]

I am doing it with relay logic, with only about 3 or 4 bits of state I can draw a complete state diagram for the thing which I just cannot do for any even slightly non trivial program running on an AVR or PIC.

Be careful of the RFI from the lamp ignition pulse if doing the micro thing, it is big, bad, and tricky to filter.

Regards, Dan.

You aint kiddin on the ignite pulses.
My similar project uses a 100 khz low pass LC filter and a 100 khz high pass LC filter, anything above 100 khz on the DC lines gets shunted into a 300 ohm load by the lc network, I cant publish the drawing, dayjob thing, But I normalized the filters to the free space impedance of 360 ohms. Load is a non inductive 300 ohm resistor.

Steve

[DMills]

For essentially similar reasons I like relays for the interlock loop, sure you can filter the input to a micro, but keeping cell phones, walkie talkies and production comms out of the micro (and KNOWING that you have under all conditions) is a hard problem, where a deliberately insensitive relay is normally pretty safe.

At an absolute minimum I would look to make heavy use of opto couplers, common mode chokes, screening cans and ferrite. A proper power supply supervisory part might also be a good plan.

Regards, Dan.

[FourDee]

And then test it while welding next to it

[allthatwhichis]

And then test it while welding next to it

When this thread was opened I would have thought they would be using the laser to weld stuff by now...

[dave]

Be careful of the RFI from the lamp ignition pulse if doing the micro thing, it is big, bad, and tricky to filter.

Regards, Dan.

Hey Dan,

What in the way of RFI suppression does the logic board have? Although I haven't really looked too closly, but I cant see much.. Is the older technology ( I think the logic board is 8088 based ) less susceptible to the RFI?

[shrad]

they do that for audio modulated tesla coils of huge power, so it shouldn't make any problems if you are grounding and shielding your board correctly, and filtering any waire which comes to or from the board

[DMills]

A stock laserscope 800 series (for example) consists of effectively 4 compartments:

Photonics, power supplies, cooling, and control board, these are pretty effectively separated by internal steel partitions which will help with the RFI issues.

The lamp supply output cable is routed from the power bay upwards in a steel box section at the rear of the machine to the photonics assembly and does not enter the control board area, and the lamp supply control cable is a screened ribbon cable (I would guess following issues during development).

Most of the IO has RC filters (on inputs) and all the cables are screened.

Finally, the logic board is based on a very slow processor by modern standards and runs at 5V as opposed to 3.3 or 1.8 which helps with the noise margin.

So, yea electro mag compatibility was evidently given some thought during the design of the thing.

Regards, Dan.

[Simon]

I am currently modifying one of my laserscopes using an Allen Bradley Compact Logix PLC.
I am using this because I had one lying around anyway and it is very immune to electrical noise and is easy to program.

This PLC will control start up and shutdown sequencing including ramping of the lamp current.
I am also using an analog output module with a driver transistor to control heating of the KTP using PWM and software interupts.
With the thermistor wired as a bridge circuit and voltage measured, I can read the temperature and perform true closed loop PID heating.
The software will only allow the laser to start if the temperature of the KTP oven is correct.

I have also added a small touch screen HMI interface to control the laser and display operating information such as power output, hours run...etc

Pictures soon