Gentec ED-200 Optical Joulemeter: Accessories

The Box o’ Optical Stuff disgorged an ancient Gentec ED-200 Joulemeter:

Gentec ED-200 - measurement setup
Gentec ED-200 – measurement setup

It’s an optical pyrometer producing, sayeth the dataplate, an output of 10.78 V per joule of energy applied to its matte black absorber. Whether it’s accurate or not, I have no way of knowing, but aiming the business end toward the sun and waving my fingers over it produced a varying voltage, so there was hope.

It has a 1/4-20 socket on one side and my spare magnetic mount expects a 3/8 inch rod, so I drilled a suitable hole in a suitable aluminum rod and cut the head off a suitable bolt:

Gentec ED-200 mounting rod - parts
Gentec ED-200 mounting rod – parts

A dab of Loctite intended to secure bushings completed the assembly:

Gentec ED-200 mounting rod - assembled
Gentec ED-200 mounting rod – assembled

I later replaced the nut with a finger-friendly nylon wingnut.

Which allows a measurement setup along these lines:

Gentec ED-200 - measurement setup
Gentec ED-200 – measurement setup

The white disk atop the sensor is a homebrewed target to indicate the active sensor area and its center point:

Gentec ED-200 target - scorches
Gentec ED-200 target – scorches

The 1 mm graticule lines give a jogging suggestion to hit the center, assuming you (well, I) manage to hit anywhere on the target at the first shot. The beam is supposed to fill most of the central region, which is obviously not going to happen here, and it must not be focused to a pinpoint. The previous owner (or his minions) put a few scars on the surface and I expect to make similar mistakes.

Early results look encouraging:

Gentec ED-200 Joulemeter - first pulse
Gentec ED-200 Joulemeter – first pulse

The SVG image as a GitHub Gist:

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I added the two mounting ears in anticipation of putting the joulemeter in the beamline between the mirrors to measure their loss.

OMTech 60 W Laser: Air Assist Flowmeter

With the solid state relay switching the air assist pump, an air flowmeter seemed like it would come in handy:

OMTech Laser - air flowmeter installed
OMTech Laser – air flowmeter installed

It’s stuck to the lip inside the top hatch on the right side of the cabinet, which may not be the most convenient location, but keeps it out of the way and doesn’t require much additional tubing.

The 6 mm tube kit included some (1/8 NPT?) push fittings that came heartbreakingly close to matching the flowmeter’s internal threads:

OMTech Laser - air flowmeter - push tube fittings
OMTech Laser – air flowmeter – push tube fittings

Given that the air pump doesn’t produce much pressure, two snippets of 1/4 inch silicone tubing suffice to couple the blue 6 mm tubing to the flowmeter’s barbs:

OMTech Laser - air flowmeter - silicone tube adapter
OMTech Laser – air flowmeter – silicone tube adapter

The run from the air pump to the flowmeter is now new blue tubing, with the original black tubing running through the drag chain to the laser nozzle:

OMTech Laser - air flowmeter - tube layout
OMTech Laser – air flowmeter – tube layout

Replacing a number of overly tight cable ties along the way may remove enough restrictions to counterbalance the additional tubing.

Opening the flowmeter’s valve all the way puts 14 l/m = 0.5 CFM through the nozzle. I have no idea of the proper rate, other than more is better while cutting and less is better for engraving.

Four years ago, Russ Sadler laid out the plumbing required to automatically select high and low flow air assist, which seems like a worthwhile project.

Kodak 750H Slide Projector: Tin Whiskers!

Mary’s folks asked me to figure out why the carousel on their Kodak 750H projector no longer turned. Some initial poking around suggested a problem with the solenoid, which only clunked when the projector was upside-down on the desk. I thought it might just have gummed up after all those years, but disassembling the thing (per the Service Manual and the usual Youtube videos) produced the root cause:

Kodak 750H Projector - broken solenoid link
Kodak 750H Projector – broken solenoid link

That explained the yellowish plastic fragments rattling around inside.

As predicted, it’s impossible to remove the solenoid without breaking the equally brittle focus gear in the process:

Kodak 750H Projector - stripped focus gear
Kodak 750H Projector – stripped focus gear

This is a sufficiently common projector to make repair parts cheap and readily available, at least for now.

Some of the interior sheet metal has a dark surface, likely heavy tin plating, covered with a thick coat of whiskers:

  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers

Touching a whiskered surface with masking tape captures the culprits, whereupon zooming the microscope and camera all the way in makes them just barely visible: they’re a few millimeters long and a few atoms wide:

Kodak 750H Projector - tin whiskers - detail
Kodak 750H Projector – tin whiskers – detail

I have surely contaminated the entire Basement Laboratory with tin whiskers. Makes me itchy just thinking about them …

OMTech 60 W Laser: Improved Electronics Bay Fan

The OMTech laser arrived with a 120 VAC fan blowing air out of the electronics bay on the right side of the cabinet. It runs continuously, because the stepper drivers remain active even when idle, and gave off an annoyingly high-pitched whirrrrr.

The Big Box o’ Fans produced a 24 V tangential blower which (felt like it) moved about the same amount of air with a quieter and lower-pitched hmmmmmm, so I made an adapter to fit it into the original cabinet opening:

OMTech laser - improved electronics fan - mounting
OMTech laser – improved electronics fan – mounting

Yeah, it’s hot-melt glued to a stacked pair of laser-cut cardboard plates. Fight me.

The white square of retro-reflective tape came from its previous life as a test item.

The black cardboard makes it rather low-key from the outside:

OMTech laser - improved electronics fan - grille
OMTech laser – improved electronics fan – grille

I reused the original grille, mostly because otherwise I’d have to put it somewhere else.

The anemometer suggests 5 m/s airflow an inch from the grille. Rounding downward from the 25×35 mm opening says it’s pulling 9 CFM from a compartment with a little over a cubic foot of free volume, which sounds enough good to me. For whatever it’s worth, this airflow calculation disagrees with all of the specs and my handwaving calculation in that old blog post.

The cabinet hatch has slits distributing the incoming air over all the active ingredients (somewhat visible inside behind the flash glare):

OMTech laser - improved electronics fan - hatch
OMTech laser – improved electronics fan – hatch

The SVG image as a GitHub Gist:

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Duct Fan: Pipe Flow Test

A crude test setup to measure the duct fan’s air flow against resistance from plausible lengths of 6 inch duct and fittings:

Duct fan test setup
Duct fan test setup

The orange stripe (upper left corner) marks the blast gate mounted on the steel plate closing off the fireplace: when the stripe is visible, the gate is open. It’s hot-melt glued into a plywood square reducing the 8 inch hole in the plate.

I won’t be using five feet of steel duct, but [handwaving] it’s what I have on hand and should produce results similar to a shorter length of flexible duct [/handwaving].

A useful conversion factor from the anemometer’s air flow in meter/sec to the corresponding volume flow in ft³/min (colloquially CFM), based on a 6 inch diameter opening with uniform airflow:

38.6 ft³·s/m·min =  0.196 ft² × 3.28 ft/m × 60 s/min

The air flow up the chimney depends strongly on basement temperature, outdoor temperature, and wind speed. On a midwinter’s calm-but-freezing evening it ran around 1.5 m/s → 57 CFM and the next day I measured 0.7 m/s → 27 CFM with wind gusts pooting old-fireplace smell into my face.

A picture being worth a kiloword:

Vent fan CFM
Vent fan CFM

The upper line is the duct fan mounted as in the picture and the lower line is the bare fan as measured on the bench.

One might reasonably conclude something has gone horribly wrong, as the ductwork seems to contribute negative resistance and increased airflow. I think it’s a combination of the natural flow up the chimney, combined with a bit of flow straightening through the pipe directing air into the fan’s blades and measuring the (mostly uniform) inlet stream instead of the (somewhat segmented) outlet stream.

Anyhow, the controller has eight speeds with surprisingly linear output. I doubt the upper line’s slope of 50 CFM/click means anything, but the consistency of both suggests a 4:1 flow range, from which I can pick the lowest speed that provides enough fume extraction.

The basement has enough air leaking in (and out) that opening the exterior door had no discernible effect on the flow through the fan and up the chimney. At top speed the fan will produce two air changes per hour, chilling the basement something awful in the winter and introducing too much warm+moist air in the summer. This may call for a separate duct for outdoor makeup air, but that’s a problem for another season.

AC Infinity Fan Air Flow

Being that type of guy, I had to measure the airflow through the inline duct fan intended for the soon-to-arrive laser cutter:

CloudlIne Duct Fan - overview
CloudlIne Duct Fan – overview

The fan is on the inlet side:

CloudlIne Duct Fan - inlet
CloudlIne Duct Fan – inlet

The outlet side consists of flow straightening blades around the backside of the motor mount:

CloudlIne Duct Fan - outlet stator
CloudlIne Duct Fan – outlet stator

The duct ports on each end are (nominal) 6 inch, with the larger central body about 7 inch ID around the blank-faced 5 inch OD motor mount.

I measured the air speed (in m/s) at the rim of the outlet port and at the center, with the rim speed about twice the center speed. The anemometer is an inch in diameter, so I assumed the annular flow was about 1.5 inch thick.

Subtracting the dead zone in the middle from the total area of the fan body gives the area of the annulus carrying most of the moving air:

Dia inchArea in^2Area ft^2
Pipe6280.20
Center370.05
Annulus210.15

Remember, the central dead zone isn’t quite dead: it has an air speed maybe half of the annulus.

More spreadsheet action finds the flow for each of the fan speed settings:

SpeedOuter m/sOuter ft/mUniform CFMAnnulus CFMInner ft/minInner CFMTotal CFMRated
11.8354705217796144
22.957111284286149888
33.874814711037418129132
44.996518914248224166176
56.0118223217459129203220
66.9135926720067933233264
77.8153630222676838264308
89.3183136027091645315351

The Uniform CFM column assumes a uniform air flow through the whole pipe, which is obviously incorrect. The Total CFM equal to the sum of the Annulus and the Inner zone, which comes out pretty close to the Rated values in the last column, taken from a comment by the seller.

Hard to believe I did the figuring before finding the “right” answers.

This is, admittedly, in free air without ducts or elbows, so the results will be lower when everything gets hooked up.