HVAC — filter monitoring and volume flow, captured mechanically

Filters age, dampers drift, volume flows shift. A ring balance delivers the current differential pressure over weeks, months, and years — no drift, no readjustment required, directly usable for filter monitoring, replacement intervals, and volume flow control.

Typical installation points

Before and after filter stages (G4, F7, F9, HEPA H13/H14)
Across dampers and volume flow controllers
Between supply and exhaust ducts
In stairwells for smoke-control overpressure (pressure ventilation)
In control cabinets to monitor filter mats

Why a ring balance fits here

HVAC is less about peak accuracy and more about long-term stability. An electronic pressure sensor in a ventilation duct is stressed by vibration, temperature swings, and humidity — drift, zero-point shift, and sensor failures follow. The ring balance is a passive mechanical measuring element: no diaphragm or spring under pressure load, no components that age or fatigue.

Filter monitoring

When pressure drop rises above a threshold, a contact switches or the 4–20 mA signal triggers a filter-change alarm.

Volume flow measurement

Combined with an orifice plate, a ring balance converts differential pressure directly into a volume flow display — square-root scale available on request.

Stairwell overpressure

Intrinsically safe variant (RW65_EX_II) for combustible environments, ATEX-certified.

Long-term stability

No drift from vibration or temperature cycles — the measuring element does not age.

Steady signal at small spans

In the typical filter monitoring range (50–250 Pa) the mechanical inertia of the ring body acts as a low-pass filter — pressure fluctuations from fan start-up or duct turbulence are physically damped. No nervous output signal, no damping parameters in the controller that can be misconfigured. At larger spans (>600 Pa) the restoring force of the calibration weight dominates and response time shortens accordingly.

Technical parameters

Typical spans

0–100 Pa, 0–250 Pa, 0–600 Pa, 0–1,800 Pa

Max. measurement error

±1.5 % FS or ±1.5 Pa

Signal output

4–20 mA, 0–10 V, switching contacts

Protection

IP54 / IP65 depending on variant

Operating temperature

−10 to +50 °C

Media compatibility

Resistant to aggressive gases and dirty air

Recommended products

RW65

pure pressure indicator for filter stations

View product

MU-Analog-65

with 4–20 mA signal to the BMS

View product

MU-Analog-65-2L

loop-powered 2-wire transmitter — when no separate supply voltage is available on site

View product

MU-Digital

with additional LCD display for filter pressure differential

View product

Rixotact 4

for closed-loop volume flow control

View product

Trusted by

In building technology, Rixen instruments are trusted by: SIEMENS AG, Honeywell, ABB, Johnson Controls, Wacker Chemie.

Your project

Volume-flow scale or filter alarm contact to your specification. Typical lead time two to four weeks ex works.

Note: The content of this page is provided for general guidance and replaces neither the operator's risk assessment nor case-by-case verification by qualified personnel. Responsibility for sizing, equipment selection, installation and operation lies solely with the operator. Despite careful preparation, we accept no liability for accuracy or completeness; the currently valid edition of the applicable regulations and standards prevails.