Pump was never broken!

16 02 2011

All photos.

Previously I though I had broken my pump.

So the pump is back from repairs. But the strange thing is when Pfeiffer received it, they said it was working fine! Although I did manage to knock the rotor out of balance and it needed fresh oil.  Here is the pump capped with a blank conflat running at full speed. GOOD.

But the problem was never the pump! The problem is a gross leak in the vacuum chamber.

Once I attach the pump to the chamber, the pump won’t spin up… indicating a gross vacuum leak.

The copper gaskets are all new, and I even got the torque wrench out to make sure the conflats were tight enough.

I can’t hear any hissing.

How do I troubleshoot this…

Here is a good overview on leak detection.



I though I head a hiss near the bellows. So I tested just the bellows and it’s working fine. So the leak is somewhere in the chamber.

Reality Check

14 02 2011

All photos.

This project has been an ongoing lesson in electrical engineering. Now with an oscilloscope I can finally see a circuit’s behavior.

I’ve spent the last week reviewing my assumptions about the most basic circuits and components. Sometime my hunches are correct, but just as often I am confounded by what I see. Here is my test setup:

The most interesting behavior happens with an AC signal. Conveniently the oscilloscope has a built in square wave generator intended for calibration. I am passing this square wave through test circuits to see how the wave changes.

The oscilloscope generates a square wave that goes from ground to +0.4 V. The frequency ranges from 50 Hz to 5 MHz depending on the time setting. I start with 50 KHz. I use two probes. The first probe is connected to the signal source, the second probe is connected to various other points in the test circuit.

The first thing to note is the signal generator doesn’t provide much power. If you overload the signal generator, you will see it’s voltage sag.

Both probes ground to the oscilloscope chassis, so choosing appropriate ground points is crucial … incorrectly grounding a probe can drastically change the circuits behavior.

I started by looking at a single capacitor. I tested this circuit:

In this capacitive coupling configuration a capacitor removes the DC component from an AC signal. Probe 2 shows the same signal as Probe 1, except shifted down. Probe 1 goes from 0 V to + 0.4V whereas probe 2 goes from -0.2 V to +0.2 V. So that’s what it looks like to block the DC component.

Next I passed the square wave through a transformer. I’m using a variable resistor to limit the current into the transformer.

This is what I see:

signal generator at top. transformer output bottom

It doubles the voltage as expected, and adds quite a bit of color to the waveform. It also draws enough current to make the signal generator’s voltage sag… even the ground line as seen in this video:

From 2011-02-12

At some frequencies, the transformer really changes with waveform:

signal generator at top. transformer output bottom

60 Hz Hum

7 02 2011

All photos.

In the US the mains power runs at 115V, 60 Hz. With an oscilloscope, I can see this mains hum everywhere. It radiates from the AC power lines throughout the lab and the whole city. Appearently our bodies make great antaneas for 60 hz: touching the oscilloscope probe shows a 9V RMS @ 60 Hz. Like a nine volt battery!  From my body!

I also noticed that the using the probe clip picks up more mains hum than just the probe tip.

I’m learning how to use the scope. I suspect it will become my main measurement tool.

Today I received a Tektronix p6109 general purpose probe compatible with my scope:

Bitcoin Fundraiser

4 02 2011

As an experiment, I’m starting a fundraiser asking for bitcoins – a new digital currency.

The project’s receiving address is:

Get the skinning on bitcoin here: http://www.bitcoin.org/

Got a powerful graphics card? You can donate without spending cash, just computer cycles! Contact me for details.

UPDATE: We have received our first donation of $1.16 BTC!!!! Awesome!

UPDATE: Another 1 BTC!

Let’s see if we can make it to 1000 BTC!!!

UPDATE: Donation of 11.24 BTC!!!  1% of goal already.

UPDATE: Another 6 bitcoins!

Digital Oscilloscope

3 02 2011

All photos.

Just received a 2430a digital storage oscilloscope. This thing is sweet.

It’s calibrated cleaned and in beautiful shape. I’m still learning how to use the thing, but just a ton of useful features.

Huge difference between the analog and digital scope. Let’s see an analog scope do this:


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