Test procedure for PHI V/F preamplifiers

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Overview:

Most of the older PHI AES systems use a voltage to frequency converter (V/F) to convert the electron multiplier auger signal output from a small current into a frequency so that the computer can count the signal. At the time these systems were designed, this was a more cost effective approach than using a high resolution A/D converter.

This document explains the procedure for testing the following V/F preamplifiers:

PHI 96

PHI 96A

PHI 96B

RBD V/F-4

Equipment needed:

(1) 30meg ohm resistor (or three 10 Meg ohm resistors soldered together)

(2) Clip Leads

(1) Computer with AugerScan

(1) Oscilloscope (optional)

(1) 4 foot BNC to BNC Cable (optional)

(1) 32-100 Multiplier Supply

Note:

The V/F Preamplifiers used on PHI systems convert the current through the electron multiplier into a frequency. The maximum current is negative 500 nA. By using a 30 Meg ohm resistor (with negative 15 volts DC applied = negative 500nA) , the negative 500 nA can be applied to the collector input without the use of a DC current source, and the V/F preamplifier easily tested.

Caution! Refer servicing of electronic units to qualified personnel.

(If this procedure is followed exactly, no high voltage will be applied to the V/F preamplifier)

 Procedure:

  1. Turn the power off on the 32-100 electron multiplier supply.
  2. IMPORTANT! Remove the HV POS IN, HV POS OUT and COL cables from the V/F preamplifier. This will prevent any high voltage from being applied to the preamplifier during testing.
  3. Set the CMA multiplier switch to OFF.
  4. Remove the cover from the V/F preamplifier:

 

preamplifier-96A-top-view

preamplifier-96A-top-view

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  1. Locate the “Collector” (J4) connection:
preamp-j4-collector

preamp-j4-collector

 

 

 

 

 

 

 

 

 

 

  1. “Jumper” a 30 Meg ohm resistor between L2 (floating minus 15 volt supply) and the COL lead (J4):
preamp-96A-col-and-L2

preamp-96A-col-and-L2

 

 

 

 

 

 

 

 

 

 

 

 

  1. Set up AugerScan to acquire a survey in the V/F mode. Make sure that V/F 1 is selected in the hardware properties and that the Auto EMS is not checked in the multiplier properties dialog box. This will force the input into the V/F mode.
  2. Turn on the 32-100 electron multiplier supply. The CMA high voltage switch should be in the OFF position. Setting the CMA voltage switch to OFF will ensure that no high voltage will be applied to the V/F preamplifier during the test. (And the cables are also disconnected)
  3. Acquire the survey and compare the results with the table below.  If you disconnect the test resistor after the survey is about half way through then you should see the counts drop to just a few thousand CPS.

 

You should have approximately the following counts displayed in AugerScan: V/F preamplifier model number Maximum V/F counts per second
PHI 96 100 kHz
PHI 96A 1 mHz
PHI 96B 1 mHz
RBD V/F-4 4 mHz

 OPTIONAL – If you have an oscilloscope you can also look at the frequency output connector of the V/F preamplifier,  Just connect a BNC cable between your oscilloscope and the Frequency output connector of the V/F preamplifier.

If the frequency output is approximately the value shown in the table above, then your preamplifier is working properly. If not, RBD Instruments provides repair services and loaner V/F preamplifiers.

When finished testing, turn off the 32-100 and replace the cables to the V/F preamplifier and set the 32-100 switch to where it was before testing (typically it is set to digital).

BONUS – Here is a link to the 96A Manual, which is the most common V/F preamplifier used on older PHI AES systems.  If you have a 96B or VF4 contact RBD Instruments.

 

11-065 28 Volt supply Check

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The 28 V DC power supply in the PHI 11-065 ion gun control can become weak and cause symptoms such as low emission current. To test the supply, measure the voltage from the red wire to chassis ground. It should be 28 volts to 29 volts DC, with less than 100mV AC ripple. When defective, the DC voltage will be low (about 10 to 16 volts) and there will be high AC ripple (3 to 6 volts).

Measure from the red wire post to the chassis.  CAUTION – refer servicing and testing to qualified personnel.

28-volt-supply-test-point

28-volt-supply-test-point

 

 

If your 11-065 28 volt supply is defective, RBD carries them in stock at all times. Contact us for more information.

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