Developing Multi Ionization Vacuum Gauges

By AZoNano

Table of Contents

Introduction
Complete Design Change
Concept of Development
Product Features
     The SH2 Multi Ionization Gauge Sensor Unit
     The SPU Pirani Gauge Detection Unit
     The SAU Pressure Sensor Unit
Conclusion
About ULVAC Technologies

Introduction

There is a growing demand for vacuum technology application products every year in the food, materials, semiconductor, pharmaceutical product and flat panel display (organic EL and liquid crystal fields and applications of vacuum technologies are expanding to solar cells, LED lights and other environmental products. In this situation, low cost vacuum gauges are needed to determine pressure in vacuum vessels and ULVAC has sold G-Tran series vacuum gauges to satisfy these needs.

A multi ionization gauge known as SH2 has been developed which is an eco-friendly hot cathode ionization transducer type vacuum gauge, as a new product joining the G-Tran series lineup.

Complete Design Change

During launch of the SH2 multi ionization gauge, the optional Pirani vacuum unit “SPU” and the pressure sensor unit “SAU” the G-Tran series vacuum gauge design was renewed. The component design which are products of the components division was also renewed as shown in Figure 2 and 3.

Figure 1. Appearance of the SH2, SPU and SAU (including gauge heads) from the left

The new product design features three symbolic colors, blue represents innovation and creativity, silver signifies accuracy and luxury and black represents reliability and strength.

Figure 2. Design concept

Figure 3. Products of new design

In order to strongly convey the features of the symbolic colors the face plates are used. The face plates previously used were rated face plates and did not stand out. Presently the model name and ULVAC logo can be seen easily and the label outline is clearer in order to create a face plate that conveys a feeling of security and reliability. The new face plates are in line with the silver tone of the vacuum pump and vacuum valve bodies and have an overall balanced design.

The controller components to measure instruments such as vacuum gauges are also matched with other products as well as the face plates in order to create a design that conveys accuracy and luxury. The contrast between the operating and display portion has been intensified to improve the user interface in terms of operability and safety.

Concept of Development

For meeting market demands for cost reduction, small footprints and simple wiring, vacuum gauges have advanced through the following stages:

  • Vacuum gauges with a combined display, control and measuring unit and a separate gauge head connected by a cable
  • Transducer type vacuum gauges that have a measuring unit combined with a gauge head without display
  • Combined transducer type vacuum gauges that have combined gauge heads and combined measuring units so they cover the low and high vacuum range.
  • The transducer type and combined transducer type have been predominantly used for large and complex systems, such as semiconductor and FPD manufacturing equipment.

In order to bring down running costs without compromising the advantages of the conventional combined transducer type vacuum gauges, a vacuum gauge has been developed that has separate gauge heads and can output pressure readings from one measuring unit as shown in Figure 4. Figure 5 shows the comparison between the new and existing combined transducer type vacuum gauge in terms of the running cost imposed by repeated replacement of the gauge head of the hot cathode ionization vacuum gauge.

Figure 4. Image of connection

Product Features

The SH2 Multi Ionization Gauge Sensor Unit

The SH2 is a hot cathode ionization vacuum gauge to be connected to a B-A type gauge head and acts as the foundation for this product series. It has the same circuit configuration as the "Qulee series" residual gas analyzer, containing an emission circuit for heating a filament and generating a certain emission current and a very small electric current detection circuit for detecting ion currents.

The gauge head comprises the same internal structure as that used in the conventional "M-10 series" metal ionization gauge head. It uses a filament made of yttria coated iridium and has a spare tungsten filament.

This unit can output a filament life warning signal, which was not available for conventional hot cathode ionization vacuum gauges until now. Iridium filaments require an increasing amount of filament current to generate a certain emission current the longer they are used. When the current supply capacity of the filament power supply is exceeded, the filament becomes unusable as shown in Figure 5. When the grid is dirty, the filament current also increases and makes the filament unusable. In this way the SH2 can measure the filament current and alert users that the filament will soon become unusable.

Figure 5. Filament current versus operation time

This unit includes an interface selectable from two types depending on the application. The interfaces include:

  • A standard interface, which has the open collector I/O control and outputs an analog voltage to send pressure readings.
  • The other is the communication interface with RS485 communication control. The standard analog type can be connected to "ISG1" 1-channel display and to "IM1R1" and "IM2R1" 4-channel displays of the G-Tran series.

Figure 6 is a photo of the standard interface. "SPU" and "SAU" connectors are respectively connected to the Pirani gauge detection unit and the pressure sensor unit with LAN cables. The filament state is indicated by the FIL LED indicator and the set point signal output states are shown by the SET-1 to SET-3 LED indicators. The MODE selector switch determines whether to operate the SH2 independently or in combination with the SPU and SAU. The ADJ button is used for adjusting the SAU pressure sensor unit. The SELECT button is used to select a voltage for pressure measurement, point setting or SAU atmospheric pressure adjustment (for the standard interface only). The communication interface is also equipped with baud rate and address set switches.

Figure 6. Standard interface

The SPU Pirani Gauge Detection Unit

The newly developed "SPU" Pirani gauge detection unit includes a CPU, unlike "GP-H" detection unit used for our "GP-1000G" and other Pirani gauges. This has enabled the use of digital signals for input to and output from the SH2, instead of analog voltages, and hence reduced reading errors caused by noise and other factors. Consequently the SPU has higher measurement accuracy than that of the older "GP-H" detection unit. The detection unit compensates for output changes caused by the ambient temperature. Furthermore, the bridge circuit is adjusted reducing the time and effort needed for adjustment and inspection.The SPU can be connected to the WP-16 (NW16) head gauge of "WP series" which has shown good performance over many years.

The SAU Pressure Sensor Unit

The G-Tran SW14 from ULVAC is capable of measuring pressures up to atmospheric pressure. It is difficult to accurately check the atmospheric pressure inside a vacuum vessel using a Pirani gauge for several reasons, such as readings depend on the type of gas being measured, measurement accuracy of ±20% at 1.0 x 10+5 Pa, fluctuation of atmospheric pressure, to achieve precise measurement, the SH2 is designed to be connectable to the SAU pressure sensor unit, which has a semiconductor thin-film element to detect the pressure inside a vacuum vessel relative to the outside air pressure by measuring resistance changes caused by strain.

Figure 7 shows the internal structure of the SAU. The semiconductor thin-film element (SUS316L) and the NW16 flange are welded so that an SAU connected to a vacuum vessel can continuously operate without causing leaks.

Figure 7. Internal structure of the SAU

Conclusion

ULVAC has improved the design of their conventional hot cathode ionization vacuum gauges and developed "SH2" multi ionization gauge, which can reduce running costs and environmental burden in comparison with existing combined transducer type vacuum gauges. It was also found that the amount of oxygen can be qualitatively determined by measuring the filament current. This means that vacuum gauges can potentially be used to detect air leaks from vacuum equipment by measuring the amount of oxygen and are expected to become more convenient instruments.

About ULVAC Technologies

Founded in Japan in 1952, ULVAC is an international corporation that designs, manufacturers and markets equipment and materials for industrial applications of vacuum technology. Today, ULVAC is a leading global supplier of production systems, instrumentation, pumps and vacuum components used in the semiconductor, flat panel display, disk/magnetic media, and industrial manufacturing markets.

The corporation is comprised of some 36 individual companies engaged in all sectors of the vacuum industry. The ULVAC name is derived from the company's conceptual foundation - "The ULtimate in VACuum Technology".

This information has been sourced, reviewed and adapted from materials provided by ULVAC Technologies.

For more information on this source, please visit ULVAC Technologies.

Date Added: Jun 13, 2013 | Updated: Jun 14, 2013
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