Absolute Pressure Transmitter with Double Chamber Vacuum Reference
1. Why You Need It
Accurate absolute pressure measurement is essential in vacuum distillation, pharmaceutical lyophilization, semiconductor processing and power plant condenser monitoring. This transmitter uses a double-chamber design with a permanently sealed vacuum reference, so it measures true absolute pressure independent of atmospheric changes. With ±0.075% accuracy and 100:1 turndown, it delivers precise, repeatable vacuum measurement that gauge sensors — which drift with the weather — simply cannot provide.
2. Working Principle
The transmitter has two chambers: one senses the process pressure, and the other is permanently evacuated and sealed to form a vacuum reference. The sensor measures the differential between the process and the fixed vacuum reference, which equals true absolute pressure. Because the reference is sealed and stable, the measurement is unaffected by ambient atmospheric pressure variation, making it ideal for deep vacuum and absolute applications.
3. Key Advantages
- True absolute pressure measurement
- Double-chamber vacuum reference
- ±0.075% accuracy
- 100:1 turndown ratio
- Immune to atmospheric changes
- IP67 protection
- Threaded mounting
- Measures liquids, gases and steam
- Ideal for vacuum processes
- Long-term reference stability
Common Pain Points & Solutions
| Problem | Conventional Issue | Our Solution | Result |
|---|
| Atmospheric drift errors | Gauge sensors drift with weather | Sealed vacuum reference | True absolute, no drift |
| Deep vacuum accuracy | Standard sensors lose accuracy | ±0.075% absolute accuracy | Precise vacuum control |
| Lyophilization control | Inconsistent vacuum ruins batch | Stable absolute measurement | Repeatable freeze-drying |
| Condenser monitoring | Inaccurate vacuum reading | High-accuracy absolute sensor | Optimized condenser efficiency |
Application Cases
Industry: Pharmaceutical
Application: Lyophilization chamber vacuum
Medium: Water vapor / air
Pressure Range: 0-100 kPa (abs)
Operating Temperature: -60 to 40 °C
Installation Environment: Freeze-dryer
Customer Challenge: Repeatable freeze-drying
Previous Problem: Vacuum drift ruined batches
Solution: ±0.075% absolute transmitter
Installation Location: Lyophilizer chamber
Result: Repeatable, validated freeze-drying
Industry: Semiconductor
Application: Process chamber vacuum
Medium: Process gas
Pressure Range: 0-133 kPa (abs)
Operating Temperature: 20-100 °C
Installation Environment: Cleanroom fab
Customer Challenge: Stable vacuum control
Previous Problem: Gauge sensor drift
Solution: High-accuracy absolute transmitter
Installation Location: Process chamber
Result: Stable, precise process vacuum
Industry: Power
Application: Condenser backpressure monitoring
Medium: Steam / condensate
Pressure Range: 0-20 kPa (abs)
Operating Temperature: 30-60 °C
Installation Environment: Power plant
Customer Challenge: Efficiency monitoring
Previous Problem: Inaccurate vacuum reading
Solution: Double-chamber absolute transmitter
Installation Location: Condenser
Result: Optimized condenser efficiency
Industry: Chemical
Application: Vacuum distillation column
Medium: Solvent / distillate
Pressure Range: 0-50 kPa (abs)
Operating Temperature: 50-150 °C
Installation Environment: Distillation unit
Customer Challenge: Accurate column control
Previous Problem: Atmospheric drift errors
Solution: Absolute transmitter, threaded mount
Installation Location: Column top
Result: Accurate vacuum column control
Technical Specifications
| Specification | Value |
|---|
| Reference | Double chamber, sealed vacuum |
| Accuracy | ±0.075% (typ) / ±0.25% FS |
| Turndown Ratio | 100:1 |
| Media | Liquids, gases, steam |
| Span Output | 50±10mV / 100±10mV |
| Protection | IP67 |
| Mounting | Threaded |
| Supply Voltage | 5 ±0.5 V DC |
FAQ
Q: What is an absolute pressure transmitter?
An absolute pressure transmitter measures pressure relative to a perfect vacuum, so its reading is true absolute pressure. Unlike gauge sensors, which measure relative to ambient atmosphere, an absolute transmitter's reference never changes. This is essential for vacuum processes, where atmospheric pressure changes would otherwise corrupt the measurement.
Q: What is the double-chamber vacuum reference?
The transmitter has two chambers: one sensing the process pressure and one permanently sealed at vacuum. The sensor measures the difference between them, which equals true absolute pressure. Because the vacuum reference is sealed and stable, the measurement does not drift with ambient conditions, providing a fixed, reliable zero point.
Q: How accurate is it?
Accuracy is ±0.075% (with an industrial ±0.25% FS option). This precision supports demanding vacuum applications such as lyophilization and semiconductor processing, where small pressure deviations affect product quality. The double-chamber reference contributes to this accuracy by providing a stable, drift-free zero.
Q: What is the turndown ratio?
The turndown ratio is 100:1, meaning a single transmitter can be ranged down to 1/100 of its full scale while maintaining accuracy. This reduces the number of span configurations needed and allows one instrument to serve a wide range of vacuum and absolute measurement duties.
Q: What media can it measure?
It measures liquids, gases and steam. This versatility makes it suitable for vacuum distillation (solvents), lyophilization (water vapor), semiconductor process gases and power plant condensers. The wetted materials are selected for compatibility with the specific process media.
Q: Why is absolute measurement needed for vacuum?
In vacuum processes, the pressure of interest is the absolute pressure inside the vessel, not the gauge pressure relative to atmosphere. A gauge sensor's reading shifts as atmospheric pressure changes, corrupting the vacuum measurement. An absolute transmitter with a sealed vacuum reference provides a true, stable absolute reading, which is critical for process control and product quality.
Q: How does it differ from a gauge pressure transmitter?
A gauge transmitter measures pressure relative to the surrounding atmosphere, so its zero shifts with weather and altitude. An absolute transmitter measures relative to a sealed vacuum, so its zero is fixed. For vacuum and absolute applications, the absolute transmitter is required; for standard open-to-atmosphere process lines, a gauge transmitter is sufficient and more economical.
Q: How is it installed?
The transmitter is installed via a threaded process connection into the vessel or line. It should be mounted to minimize vibration and temperature effects, and the electrical connection wired to the 5 V DC supply and span output. Calibration is performed against a vacuum reference to establish the correct zero and span.
Q: Is it suitable for lyophilization?
Yes. The ±0.075% accuracy and stable vacuum reference make it ideal for pharmaceutical lyophilization (freeze-drying), where the vacuum level directly affects sublimation rate and product quality. A stable absolute measurement ensures repeatable, validated freeze-drying cycles.
Q: Where is it used?
It is used in pharmaceutical lyophilization, semiconductor process vacuum, power plant condenser monitoring and chemical vacuum distillation. Anywhere a true, stable absolute pressure or deep vacuum measurement is required, the double-chamber absolute pressure transmitter provides the accuracy and reliability needed.
