Spectroil M, M/N, M/C and M/F
Solid State Excitation Source Upgrade

Subject: Upgrading the Spectroil M Oil Analysis Spectrometer with a Solid State Excitation Ignition Module and SFTM Port

Objective
This improvement upgrade to the Spectroil M incorporates a solid state excitation ignition circuit which provides improved stability, and a means to monitor the source frequency without opening the instrument, facilitating user maintenance.

Background
The Spectroil M Oil Analysis Spectrometer uses an oscillating alternate current (AC) electric arc discharge excitation source which has been optimized for oil matrices. The excitation source is the most important subassembly of the spectrometer with regard to analytical performance (accuracy and repeatability).

The excitation source has two basic functions: 1) to provide a high voltage potential to overcome the resistance offered by the air and oil between the graphite rod and disc electrodes which make up the analytical gap, and 2) to provide an analytical potential capable of instantaneously vaporizing the oil and any wear or contaminant particles suspended in the oil. This is accomplished with a free running excitation source utilizing a high voltage transformer to charge a capacitor to a potential high enough to ionize the air between the graphite electrodes of the analytical gap. Once the high voltage has ionized the air across the analytical gap, the resistance of the gap is effectively zero ohms, or a short circuit to ground. This momentary (approximately 3 microsecond) short circuit is all that is necessary to discharge the potential which is stored on the analytical capacitor. This potential will instantaneously vaporize the oil and any particles which are suspended in the oil. The vaporization potential will raise the energy level of the valence electron(s) of the particles. When this energy is released as the electron(s) return to the ground state, it will create atomic emission, which is the basis of this technique.

This process occurs approximately 900 times per second and is referred to as the excitation source frequency. The excitation frequency is free running, which means it is not regulated or electronically controlled. In order to adjust this frequency and still maintain optical alignment between the analytical gap and the optical processing assembly, a second gap called the auxiliary gap is designed into the excitation source in series with the analytical gap. The main adjustment for the source frequency is the size of the auxiliary gap.

This excitation source frequency has become the standard for wear metal analysis, particularly in the United States Department of Defense (DoD) Joint Oil Analysis Program (JOAP).

The excitation source frequency of all free running AC arc emission spectrometers is affected by six parameters, physical and environmental. They are:

• condition/gap distance of auxiliary gap electrodes
• stability of the AC line voltage
• frequency of the AC line voltage
• component tolerances within the excitation source itself
• relative humidity
• elevation (barometric pressure)

The upgrade will make the Spectroil M immune from the six parameters and provide a fixed regulated frequency. It replaces the ignition transformer and four resistors with a solid state module. It also installs an external port for the Source Frequency Test Meter (not applicable for M/N (MOD-1) instruments) to allow monitoring of the source frequency without removing the instrument's panels.

Benefits of the Upgrade
The solid state excitation ignition module was developed by Spectro Inc. to minimize the need for the operator to monitor and adjust excitation source frequency. It consists of a complete module which generates and precisely controls excitation source frequency. It has been successfully tested in high sample throughput environments at many commercial laboratories and at the Joint Oil Analysis Program Center (JOAP/TSC). It is currently being installed in all U.S. Air Force Spectroil M's, and has been incorporated as an engineering change into all instruments delivered by Spectro Inc. since April, 1997.

The main advantage of the solid state excitation ignition circuit is that it virtually eliminates the need to adjust excitation source frequency. Its output is a fixed frequency which is not dependent on auxiliary gap size, voltage or frequency fluctuations, or environmental changes. The solid state excitation ignition circuit thus provides better long term stability and eliminates the requirement for the operator to readjust source frequency. It also allows checking of the frequency without exposing live electrical circuitry. By eliminating these tasks it reduces the possibility of inaccuracies due to operator error.

Cost of the Upgrade
The upgrade can normally be performed within one eight hour working day. Once the upgrade has been completed a complete analytical check up of the instrument will be performed. Please contact the Operations Department for a quotation.