Tag Archives: mcd

Amplifier Discriminator Tests

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One of the troubleshooting techniques that can be used to test the counting circuitry of an auger or XPS system is called “tickling the brick”.   The term came about from when the early PHI systems used the Princeton Applied Research (PAR) 1120 amplifier discriminator for pulse count detection of electrons. The 1120 kind of looked like a brick, and so the term “tickling the brick” was born.

Basically, tickling the brick tests the brick (amplifier discriminator) and the counting circuitry.   This is one of the first troubleshooting steps that you would take if you are not getting any counts at all with your auger, XPS or SIMS system.

The 1120 amplifier discriminator is still in use on many PHI systems, as is its newer replacement, the 1182.  The 1120 and 1182 are used with single channel detectors.

In addition to the 1120 and 1182 amplifier discriminators, the “tickling the brick” concept can also be applied to PSD and MCD detectors on XPS systems.

The procedures for each amplifier discriminator type are described below.

Amplifier-Discriminator

1120/1182 Test Procedure

  1. Set up a alignment (can be any range) and select the 1120/1182 as the signal input. For most PHI systems using AugerScan software, that will be PC1 input in the hardware properties dialog box.
  2. Remove the bnc input that goes between the analyzer and the 1120/1182
  3. Turn off the analyzer control and electron multiplier supply as they are not needed.
  4. Start the alignment acquisition and then stick a piece of wire into the bnc input of the 1120/1182. This wire will act like an antenna and you should see between 20 million and 30 million CPS of noise.
  5. Remove the wire and the counts should go to zero.

If the counts behave as expected then both the 1120/1182 and the counting circuitry are working properly.

PSD Position Sensitive Detector Preamp Test Procedure

PSD

PSD

 

 

 

 

 

 

 

 

  1. Set up an alignment (can be any range) and select the PSD as the signal input. For most PHI systems using AugerScan software, that will be the PSD input in the hardware properties dialog box.
  2. Turn the card rack power OFF.
  3. Remove the bnc inputs to the PSD that goe between the analyzer and the PSD. These are the little white wires that go from Preamps A and B to the analyzer.
  4. Connect a test clip to the center pins of each of the little white wire bnc connectors.
  5. Start the alignment acquisition and then with your fingers touch the ends of both of the test clips that go to the center pins of each of the little white wire bnc connectors. The test clips will act like an antennae and you should see about 50K to 80K CPS of noise. Both clips need to be touched at the same time. NOTE: The clips go to the wires, not the BNC connectors on the analyzer.
  6. Remove the test clips and the counts should go to zero.

If the counts behave as expected then both the PSD preamp and the counting circuitry are working properly.

Make sure that the card rack power is OFF when you reconnect the PSD cables to the analyzer.

MCD Amplifier/Discriminator Test Procedure.

MCD

MCD

 

 

 

 

 

 

  1. Set up an alignment (can be any range) and select the MCD as the signal input. For most PHI systems using AugerScan software, that will be the MCD input in the XPS hardware properties dialog box.
  2. Turn the card rack power OFF.
  3. Unscrew the MCD amplifier discriminator from the analyzer flange and carefully remove it. NOTE: Use care when reinstalling it after the test procedure to make sure you do not bend any pins. Also make sure that the card rack power is OFF when you reinstall the amplifier discriminator on the analyzer flange
  4. Turn on the card rack power and start the alignment.
  5. There are 20 socket connectors visible on the end of the MCD amplifier discriminator. Each of those connectors (except for the middle 4) represents one of the 16 channels that are connected to the MCD detector inside the analyzer.
  6. Start the alignment acquisition and then stick a wire into each of the open pins on the end of the MCD preamp, one at a time. The test clips will act like an antennae and you should see about 20K to 80K CPS of noise when the clip is inserted.
  7. Remove the wire and the counts should go to zero.
  8. Repeat steps 6 and 7 for each of the other pins on the end of the MCD amplifier discriminator.

If the counts behave as expected then both the MCD amplifier/discriminator and the counting circuitry are working properly.

Multi channel detector continuity tests

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The multi channel detector (MCD) assembly found on Physical Electronics 5500 through 5800 X-ray photoelectron spectroscopy (XPS) systems comprises two pieces – the channel plate assembly and the connection flange.

If you follow the procedure in the 10-360 spherical capacitive analyzer manual you can replace the channel plates (Chevron type) without too much difficulty. Two things to remember are to use some small Allen wrenches to hold the pins up (that removes the spring tension) and to make sure that the little marks on the channel plates face each other.  This drawing might be helpful – MCD detail

But equally important as installing the channel plates correctly is ensuring that you have good continuity on all of the pins on the connection flange, and that you are making a good electrical contact with the channel plate assembly when you install the flange.

Before you install the connection flange, short out the pins on the connector flange with aluminum foil as shown in the pictures below. Then use an ohmmeter to measure the continuity of each pin to the flange. Each pin should have a resistance of less than 2 ohms. Sometimes the pins can become oxidized and if so the resistance can be high, as high as Meg ohms. If the resistance on one or more pins is high, very carefully use a tweezers and pull up on the wire on the end that is close to the connector. Move it no more than 1/16″ up and down. If you move it up too high, the pin will come off the connector pin and it is very difficult to put those back on. Verify that each pin has good continuity and is all the way down before installing the connection flange.

When you install the connection flange (after first installing the channel plate assembly inside the SCA) measure the capacitance of each pin to the chamber. They should all have the same capacitance, typically about 250 pf. The 4 middle pins are not used so their capacitance will be about 100 pf. If the other 16 pins do not all have the same capacitance, then the some of the spring contacts are not making contact with the channel plate assembly. Try rotating the flange a little bit. You may need to slide the connection flange back a little bit and then reseat it. Just be sure that each pin has the correct capacitance before tightening the connection flange.

Finally, the pins on the connection flange may have been bent slightly during the continuity test. Visually inspect the pins and carefully slide on the MCD preamp to make sure that it will go on without bending any of the pins. Adjust the pins as needed until the MCD preamp can go on easily. The pins on the connection flange are very soft and can bend easily. It is possible to force the MCD preamp down on a bent pin and if so, the pin will usually break when you try to straighten it. So just be aware that this and you will not bend the MCD pins.

 

RBD Instruments provides the MCD channel plates and technical support to help you with the installation.

 

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MCD pins
MCD spring contact pins