Micromanometer
A micromanometer is a device used for measuring very small pressure differences, typically in
the range of millimeters (mm) or fractions of millimeters of water column (H2O).
Working Principle:
There are two main types of micromanometers:
1. Liquid Column Micromanometer: This is the traditional design. It consists of a U-
shaped tube partially filled with a sealing liquid, commonly water or mercury. One end of
the U-tube is connected to the pressure source with the higher pressure, and the other end
is connected to the lower pressure source or left open to the atmosphere (for gauge
pressure measurement). The pressure difference causes the liquid levels in the two arms
of the U-tube to differ. The height difference between the liquid columns is directly
proportional to the pressure difference.
2. Electronic Micromanometer: This is a modern version that utilizes a pressure sensor to
convert the pressure difference into an electrical signal. The signal is then processed and
displayed digitally on a screen, providing a more precise and convenient measurement.
Calibration:
Calibration of a micromanometer involves using a reference pressure source with known
pressure differences. The micromanometer readings are compared to the known values, and any
necessary adjustments are made to the scale or internal components (for electronic models) to
ensure accuracy.
Advantages:
• High sensitivity for measuring very small pressure differences.
• Simple design for the liquid column type (easy to understand and maintain).
• Relatively inexpensive, especially for the liquid column type.
• Direct visual observation of pressure difference (liquid column type).
Disadvantages:
• Limited measuring range compared to other pressure gauges.
• Can be susceptible to temperature fluctuations that affect the sealing liquid density.
• Requires level placement for accurate readings (liquid column type).
• Electronic models can be more complex and expensive.
Applications:
• Measuring pressure drops across filters and valves in air and gas flow systems.
• Calibrating other pressure instruments.
• Monitoring pressure in cleanrooms and laboratories.
• Duct static pressure measurement in HVAC systems.
• Differential pressure measurement in medical devices (e.g., respirators).
Ring Balance Gauge
A ring balance gauge is a type of pressure measurement instrument that utilizes the concept of
balancing forces to determine the pressure difference between two points.
Working Principle:
1. Construction: The gauge consists of a hollow, ring-shaped body that can freely rotate on
a central axis. This ring is partially filled with a sealing liquid. A partition divides the ring
body into two chambers.
2. Pressure Application: The pressure to be measured (often a differential pressure) is
applied to the two chambers through separate tubes.
3. Force Balance: The pressure difference creates a torque on the ring, causing it to rotate.
This rotation is countered by a weight attached to the ring at a specific location.
4. Pressure Measurement: As the ring rotates, the weight moves until the torque caused by
the weight balances the torque caused by the pressure difference. The amount of rotation
(measured by the position of the ring) is then correlated to the pressure difference.
Calibration:
Calibration of a ring balance gauge involves applying known pressure differentials and recording
the corresponding ring positions. This data is used to establish a calibration curve that translates
the ring position into the actual pressure difference. There are external adjustments that can be
made to fine-tune the gauge's accuracy.
Advantages:
• High accuracy, especially for low differential pressures.
• Wide range of measurable pressures depending on the design.
• Can measure absolute or gauge pressure depending on the reference pressure used.
• Less susceptible to clogging compared to some other differential pressure gauges.
Disadvantages:
• More complex design compared to simpler gauges like diaphragm gauges.
• Requires careful handling due to the presence of moving parts and sealing liquid.
• Limited acceptance in some regions (more common in Europe than the US).
Applications:
• Airflow measurement in HVAC systems.
• Pressure measurement in cleanrooms and laboratories.
• Monitoring pressure across filters.
• Level measurement in tanks (by measuring pressure difference between top and bottom).
• Leak detection in pressurized systems.
