THERMOVAC MEMS Vacuum Gauge Guide

Leybold THERMOVAC series MEMS Pirani vacuum transmitters: a complete guide to selection, installation, and troubleshooting

Introduction: When traditional Pirani vacuum gauges cannot meet modern process requirements

In the field of vacuum technology, the accuracy of pressure measurement is directly related to process quality and equipment safety. The traditional Pirani vacuum gauge uses slender hot wires as sensing elements, which are prone to damage due to vibration, impact, or contamination, and have limited response speed. Leybold's THERMOVAC series (TTR 91 N, TTR 96 N, TTR 911 N, TTR 916 N) uses advanced MEMS Pirani solid-state sensors to apply microelectromechanical systems (MEMS) technology to thermal conductivity vacuum measurement. This sensor is composed of heating resistor elements on a silicon chip, which has significant advantages such as anti vibration, anti impact, fast response, and high repeatability. In addition, the coating version (C model) uses Parylene HT coating, which significantly improves its chemical corrosion resistance and is suitable for harsh process environments.

This article is based on the THERMOVAC series product data manual, providing a detailed technical guide from technical principles, model comparison, installation and wiring, gas correction, digital interfaces, fault diagnosis to maintenance and calibration, to help engineers correctly select and use in replacing old models or building new systems.

Principles and advantages of MEMS Pirani technology

1.1 Differences between Traditional Pirani and MEMS Pirani

The traditional Pirani vacuum gauge utilizes the relationship between the heat loss of a hot wire (usually tungsten or platinum) and gas pressure. As the pressure decreases, the number of gas molecules decreases, the heat dissipation of the hot wire deteriorates, the temperature increases, and the resistance changes. This method is simple and reliable, but the hot wire is slender, prone to breakage, sensitive to vibration, and has a large heat capacity, resulting in a slow response.

The MEMS Pirani sensor integrates heating resistors onto tiny silicon membranes and is manufactured using microfabrication technology. Its advantages include:

Extremely high mechanical strength: Silicon chips can withstand severe vibrations and impacts without the risk of filament breakage.

Quick response: The small thermal mass makes the thermal equilibrium time extremely short.

Low power consumption: Operating power consumption<1.2 W.

Good repeatability: The semiconductor process ensures consistency.

Small size: The sensor size is only a few millimeters, which is conducive to integration.

1.2 Measurement principle

THERMOVAC transmitters are based on the principle of thermal conductivity measurement. The heating resistor in the MEMS Pirani sensing unit is subjected to a constant power, and its temperature depends on the thermal conductivity of the surrounding gas. The higher the gas pressure, the higher the thermal conductivity, and the lower the resistance temperature. By measuring the resistance value (or the power required to maintain a constant temperature), the gas pressure can be inferred. The output signal is linearized to provide a voltage proportional to the logarithm of pressure.

1.3 Coating version (C model)

For corrosive process gases such as halogens and acidic gases, the metal and silicon surfaces of standard MEMS Pirani sensors may be corroded. Parylene HT is a high-performance polymer coating with excellent thermal stability (able to withstand 350 ° C for short periods of time) and chemical inertness. The sensors with coated versions (TTR 911 CN, TTR 916 CN) have been coated with Parylene HT, significantly improving their corrosion resistance and making them suitable for harsh chemical processes.

Detailed explanation of product series and models

The THERMOVAC series includes multiple models, covering a wide range of needs from basic analog outputs to advanced digital interfaces.

2.1 TTR 91 N (No Switching Output)

Measurement range: 5.0 × 10 ⁻⁵~Atmospheric pressure (1000 mbar)

Output: Analog voltage (logarithmic characteristic)

Interface: Analog only

Vacuum connection: DN 16 ISO-KF, ⅛ "NPT, DN 16 CF (can be baked to 85 ° C)

Applicable scenarios: General coarse/medium vacuum measurement, connected to a controller (such as PLAY ONE/GRAPHIX ONE)

2.2 TTR 91 SN/TTR 96 N (with switch output)

TTR 91 SN: 2 set point relays (SP1, SP2), DN 16 ISO-KF or NPT

TTR 96 N: 2 set point relays, coated sensor (Parylene HT), suitable for corrosive media

Switch range: 2.7 × 10 ⁻⁴~1000 mbar

Contact capacity: 1 A @ 30 V AC/DC (resistive load)

Contact life: ≥ 100000 times under 1A load; ≥ 2000000 times under 0.2 A load

Applicable scenarios: requiring on-site interlocking, alarm or control (no PLC required)

2.3 TTR 911 N/911 SN/911 CN (digital interface model)

TTR 911 N: Equipped with LCD touch screen display, displaying pressure values, units, and set point status. No digital interface.

TTR 911 SN: with RS 232 interface (+3 set point relays), can be used for communication with PC or PLC.

TTR 911 CN: with EtherCAT or Profibus interface (coated sensor), suitable for industrial fieldbus networks.