Antares Analytical Bulletin for July 2002

Subject:  Loss of High Voltage (also called HV)

Relevant Units:  All FSQ, all DV with MC20 and all ICP with MC20 readout. Certain HA10-12 and Labtest spectrometers with MC20 upgrade will be noted where appropriate. This does not cover the DV6E or Foundrymate which use a different power supply and interlock system.

Relevant Matrix: Not Applicable

Symptoms:

1. No HG signal on panel mounted HG meter, no Hg reading on the computer screen during optical alignment (later FSQ models without a panel mounted vacuum meter), no element signal while aligning (number is less than 10) … DV6 only which uses an element line, not an Hg bulb for optical alignment
2. BAIRDAS program shows red in HV box of the Routine Analysis screen of the program
3. Sudden inability to get accurate analytical results. See April 2002 Bulletin for more information on this.
4. HV LED on the MC20 front panel is out

Background Information

1. Do not automatically assume because there is no high voltage, the high voltage supply is bad. There can be several possible reasons for no high voltage.
2. Almost all FSQ / DV, ICP series units are vacuum units, but there are a limited number of airpath (no vacuum pump) DV /  FSQ units installed at various customer sites. All HA10/12 units are air path.
3. Where air units are different from vacuum units, the differences will be explained, otherwise all information will be applicable to vacuum and airpath units. Except where information is applicable to all types, most of the information will be used only as background for the HA10-12 units.
4. The high voltage power supply, located in the left front slot of the MC20, is interlocked in several different ways, depending on the spectrometer. Please verify which spectrometer configuration you have (Vacuum DV, airpath FSQ etc) and find the correct selection listed later in this bulletin.
5. The high voltage in interlocked primarily to protect the PMTs (photomultiplier tubes – please see June 2002 Antares Tech Bulletin) from damage in case of loss of vacuum in the optical cell. This is not a concern in the air path units.
6. Another reason for the high voltage interlock is optical. As the unit pumps down, the vacuum cell “stresses” and optical dispersion shifts. A further explanation of this “dispersion shift” isn’t necessary here. This “dispersion shift” is calculated into the spectrometer design and for correct analytical results, the vacuum spectrometer must be operated at vacuum. This is not a concern for air path units.

Basic High Voltage System:

1. The High Voltage Power Supply is a step up transformer which takes 24 VAC from the Torroidal transformer, steps it up to 1000 VAC,  rectifies / inverts to –1000 VDC, filters and exports to the Motherboard of the MC20.
2. This 24 VAC supply  voltage is run through the set of contacts on the K1 relay located on the high voltage power supply.
3. The K1 relay is energized, and contacts closed, when the correct interlock signal is received from the spectrometer.
4. The 24 VDC for the interlock circuit is generated within the MC20 and sent to the spectrometer interface board.

Basic Interlock Systems by Type

1. The DV2 to 5 series, all ICP Series, and earlier FSQ with a front panel mounted vacuum gauge: The high voltage will be interlocked through the contacts on the back of the vacuum gauge. The on / off of the high voltage is controlled by the vacuum pressure in the cell letting (or not letting) the red indicator needle fall below the 2^nd black HV set point needle. The set point needle on the vacuum gauge which indicates vacuum pressure, opens and closes contacts within the vacuum gauge.
2. DV6 / FSQ with no vacuum gauge: The high voltage is interlocked through the electronic set point on the vacuum thermocouple. This is a factory adjusted setting. When vacuum pressure in the cell is low enough, an electrical control signal is sent down to the high voltage power supply to turn on.
3.  DV / FSQ Air Path units:  For these units the vacuum interlock is wired permanently closed and high voltage will be present at all times unless the MC20 or high voltage power supply are turned off.
4. HA10 / 12: The high voltage interlock are 2 switches, wired in series, which close as soon as the top optical cover is put in place and fastened down correctly and tightly. 

Possible Causes and Solutions:

High Vacuum Pressure (> 100 microns) or no Vacuum: 

• Check to be sure your vacuum level (red needle on the vacuum gauge) is below the 2^nd (black) set point on the older knob type vacuum gauges.
• Push the “high set point” button on the newer Pirani type vacuum gauges. This set point should be about 50 and the red indicator needle should be below it.  
• Solution: Check for correct operation of the vacuum system. Be sure the vacuum pump is operating and the gate valve is open. More will be covered on the DV / FSQ / ICP vacuum systems in the Antares Tech Bulletin in August.

Bad Thermocouple: The thermocouple may  not be putting out voltage to the high voltage power supply interlock (FSQ & DV6 without a vacuum meter). Thermocouple may not be putting correct reading to the vacuum gauge (front panel mounted vacuum meters … ICP, DV2-5 and FSQ). Please contact Antares Analytical for further help in testing.

Bad Vacuum Meter: The spectrometers which use a front panel mounted vacuum meter have the HV interlock signal going through one set of set points inside the meter. This set point is manually adjusted from the front meter and is normally the higher of the 2 black needles. Inside the gauge are a set of mechanical contacts which are closed when the vacuum indicator needle moves below the 2^nd set point, closing the HV interlock circuit. It is common for these contacts not to close even though the red indicator needle is lower in pressure than the HV interlock set point. This is a common problem on some older units (DV4 and early FSQ for example). This is not repairable and contact Anatres Analytical for advice.

Bad HV Power Supply: There are several things to check on the HV power supply

·         The K1 relay has been a common failure in the past. If the relay is suspected, replace from your stock and try again.

·         There are 6 fuses on the HV power supply. Check to be sure all are good and replace any bad ones, with new fuses from stock.

·         Further than this please contact Antares Analytical for troubleshooting the HV Power Supply Board.

Bad Low Voltage Power Supply (MC20): Please contact Anatres for further advice

Bad Torroidal Transformer (MC20): Please contact Antares for further advice.

______________________________________________________________________

This Technical Bulletin is written by Gerry Smith, Technical Services Manager of Antares Analytical. Having spent 22 years with Baird in various capacities, including many years as Final Test / Calibration Manager and Senior Service Engineer, International Operations, he is well qualified to answer any Technical or Applications problems you may have.

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