John Morris

Overview

The HPS® Series 925 and 925 Compact (925C) MicroPirani™ transducers are thermal conductivity gauges based on a unique, MEMS-based sensor. The 925 and 925C are commonly used for vacuum pressure measurement applications in semiconductor and analytical environments, as well as general vacuum applications.

The Series 925 and 925C sensors offer a wide measurement range from 0.00001 Torr to atmosphere and are based on measurement of thermal conductivity in a small cavity where gas enters by diffusion only, instead of flow.

While traditional Pirani gauges often have problems with temperature drift, low accuracy, calibration and sensitivity to mounting position, these issues are significantly reduced with the Series 925 and 925C Micro Pirani™ sensors.

The sensor element in the 925/925C is made of a one millimeter square silicon chip, allowing the measurements to be made in a very small volume. Due to the small size and repeatable geometry of the sensing portion of the MicroPirani™, it has a range from ATM down to 0.00001 Torr. The design minimises the effects of convection, so operation is possible in any position without compromising accuracy, simplifying installation.

The sensor's solid state design is highly resistant to vibrations and mechanical force, resulting in less system downtime due to broken filaments.

Digital communication allows for all adjustments and monitoring to be delivered real-time, via a host computer. The 925/925C includes RS485 or RS232 communication as a standard feature.

The 925 has a 15 pin connector, while the 925C has a 9 pin connector. The 925 and 925C are also equipped with 1-9 VDC analog output. For process control, the 925 has three setpoints, and the 925C has one setpoint relay, which can be set, adjusted and monitored through the digital port.

Like all thermal conductivity sensors, the 925 and 925C are sensitive to gas type. To compensate for gas dependency, the MicroPirani has a number of common gas calibrations that can be selected via digital interface. This makes it a simple solution for locating medium to fine leaks in vacuum systems.
Features

Series 900 Ethernet Gateway
The 925 and 925C are compatible with the Series 900 Ethernet Gateway. The Ethernet Gateway is designed exclusively for operation with the entire range of HPS Series 900 vacuum transducers. Converting the digital output to Ethernet, the Gateway enables any
of the Series 900 transducers to operate via Ethernet communications. By connecting multiple RS485 transducers to one Gateway, the Ethernet Gateway offers a cost effective solution to system integrators looking to use multiple vacuum transducers on a single system.

Benefits

• Increased pressure measurement range from 0.00001 Torr to atmosphere, two decades beyond a standard Pirani
• Setpoint relays have a fast response time for reliable process control
- 925C has one setpoint relay
- 925 has three setpoint relays
• Compact dimensional design
• High accuracy and reduced process cycle time
• Ease of operation via analog output and digital communication
• MicroPirani™ solid state sensor is resistant to damage from air inrush or vibration
• Mountable in any orientation for ease of installation; no loss of measurement accuracy
• CE marked, compliant with EMC Directive 89/336/EEC