Which measuring ranges do the transmitters cover?

All combinations between ±20 Pa and ±1,800 Pa; the smallest measuring span is 40 Pa. Common ranges are −50…+50 Pa, 0…50 Pa, 0…100 Pa, 0…500 Pa and 0…1,000 Pa. The measuring range is specified at order. The ring balance is not designed for spans above 1,800 Pa — that range lies outside the Rixen programme.

How quickly does a ring balance transmitter respond to pressure changes?

It depends on the measuring span. At small spans the calibration weight is light and the restoring force is low — the response time is several seconds. The sealing liquid acts as a mechanical low-pass filter, smoothing out pressure spikes and turbulence; the output signal stays steady without damping parameters in the controller. At large spans the calibration weight is heavier and the response time shortens significantly. For room pressure control and filter monitoring the behaviour is adequate across all spans.

Can the three outputs be used at the same time?

Yes. On the MU-Analog-65 and the MU-Digital, all three outputs — 4–20 mA, 0–20 mA and 0–10 V — are standard and available in parallel. The MU-Analog-65-2L, as a 2-wire device, provides the passive 4–20 mA output only.

What happens during a power outage?

The electrical outputs are inactive without supply voltage; on the MU-Digital the LCD goes dark as well. The mechanical measuring element retains its position — once power is restored, the reading is immediately available again. The analogue 150×150 mm scale of the MU-Analog-65 and the MU-Analog-65-2L remains permanently readable even without power.

Are the transmitters approved for ATEX zones?

No. The MU-Analog-65, MU-Analog-65-2L and MU-Digital have no ATEX certification. For hazardous areas, Rixen offers the RW65_EX_II: an intrinsically safe differential pressure gauge (II 1 GD Ex ia IIC/IIIC T4 Ga Da) with a passive 4–20 mA output, approved for Zones 0/1/2 and 20/21/22. It is connected via an isolation stage on the safe side.

What was the MU-Analog-65-EX and why was it discontinued?

The combination of a ring balance and a downstream Ex transmitter — previously offered as the MU-Analog-65-EX — worked reliably for decades. In recent years, however, inspection practice has become stricter: the ATEX classification of the ring balance is increasingly scrutinised and can vary from one inspector to the next. For operators, this meant planning uncertainty. The RW65_EX_II was therefore developed specifically as a fully approved device for Ex applications — making its compliance documented and independent of individual assessment. The RW65_EX_II has the intrinsically safe 4–20 mA 2-wire transmitter built in.

How often does a differential pressure transmitter need to be calibrated?

All three devices ship with a factory calibration. The drift-free mechanical measuring element does not shift in operation — calibration histories typically show no deviations. This is the basis for significantly extended calibration intervals under ISO 9001 and GMP Annex 1: fewer OOS events and less validation effort during routine checks. The specific interval is defined by the operator within their quality management system.

How do I select the display unit?

Available units are Pa, kPa, daPa, mbar, mmWS, mmCE and in.W.C. The unit is specified at order and set at the factory — as a printed scale graduation on the MU-Analog-65 and MU-Analog-65-2L, and as the fixed display unit of the LCD on the MU-Digital. On the MU-Digital, the unit cannot be changed afterwards.

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Products / Transmitters

Differential Pressure Transmitters for Low Pressure — from 40 Pa

A differential pressure transmitter measures the difference between two pressures and converts it into a standard electrical signal — 4–20 mA, 0–20 mA or 0–10 V. In building services and plant engineering the device is often simply called a pressure transmitter — for filter monitoring, cleanrooms and volume flow measurement this almost always means a differential pressure transmitter capturing the difference between two measuring points. Rixen transmitters are designed for the smallest pressures: measuring spans from 40 Pa to 1,800 Pa, measured with a mechanical ring balance instead of an electronic sensor. Max. error: ±1.5 % FS (> 100 Pa) or ±1.5 Pa (< 100 Pa).

How does a differential pressure transmitter work?

At Rixen, measurement is separated from signal conversion: measuring is purely mechanical, converting is electronic. The signal chain has three stages.

Mechanical measuring element

The pressure difference acts on a pivoted ring body and works against the weight of a calibration weight. The ring body rotates until both forces are in balance — the rotation angle is the measure of the differential pressure. At small measuring spans, the sealing liquid acts as a mechanical low-pass filter: pressure spikes and turbulence are damped physically.

Contact-free sensing

A Hall sensor reads the rotation angle of the ring body — not the pressure. The pressure measurement itself contains no diaphragm, no spring and no pressure-stressed components that can age, fatigue or become brittle.

Standard signal

The transmitter converts the rotation angle into a standard electrical signal: 4–20 mA, 0–20 mA or 0–10 V — depending on the device, active with its own supply or passive, powered via the current loop. The signal feeds building management, SCADA or a PLC.

This division of labour is the core of the concept: electronic differential pressure sensors have documented drift rates of 0.2 to 1 % of full scale per year and require periodic recalibration. In a ring balance transmitter, the measurement sits in the mechanical element — no ageing component in the measurement path, physically zero drift, no drift-induced readjustment. The transmitter only converts the rotation angle; it is not itself the sensor. Why electronic transmitters reach minimum ranges only via stretched sensors (“turndown”) and what that means for long-term stability is explained in the article Ring balance vs. electronic sensors.

Transmitter, indicator, switch, controller — the distinction

“Measuring transducer”, “pressure transmitter” and “transmitter” mean the same thing: a device that converts the measured value into a standard electrical signal. Alongside it stand three related device types — the distinction decides which device the application needs.

Differential pressure indicator

Shows the pressure difference on the 150×150 mm scale on site — no electronics, no signal output, operates without power supply.

RW65View product

Pressure switch

Switches at limit values: the RW65 is available to order with up to two switching contacts — as MK contacts (magnetic spring) or IK contacts (NAMUR, inductive), one type per device.

RW65 with MK/IK contactsView product

Differential pressure transmitter

Converts the reading into a standard signal for BMS, SCADA or PLC — 4–20 mA, 0–20 mA or 0–10 V. The three devices on this page.

MU-Analog-65 · MU-Analog-65-2L · MU-Digital

Differential pressure controller

Measures and controls in one housing: 0–10 V transmitter output plus a three-point step controller (relays open/close/hold) for classical damper drives.

Rixotact 4View product

Which transmitter fits? Two decisions

All three devices use the same ring balance measuring element and deliver the same accuracy. The selection comes down to two questions: how is the device powered, and which local display is required?

Loop-powered (2-wire) or separate supply?

2-wire, loop-powered

MU-Analog-65-2L

Passive transmitter — supply 11–30 V DC via the signal line, no separate power supply
One output: 4–20 mA
Loop resistance max. 600 Ω at 24 V DC
For retrofit with existing 2-core wiring, few spare terminals, long cable runs

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Separate supply (active)

MU-Analog-65 · MU-Digital

Supply voltage selected at order: 24 VAC · 110 VAC · 230 VAC · 24 VDC
Three outputs in parallel: 4–20 mA, 0–20 mA and 0–10 V — all standard
For BMS and SCADA integration when several signal types are required

View product

Analogue scale or LCD?

Analogue scale

MU-Analog-65 · MU-Analog-65-2L

150×150 mm scale, readable from several metres away
Readable even without supply voltage — for example during a power outage
Scale graduation in the unit selected at order

View product

LCD

MU-Digital

3½-digit LCD, character height 12.5 mm — numeric value directly at the device
Useful for commissioning and spot-checks without a test instrument
Requires supply voltage; display unit set at the factory

View product

The three transmitters compared

	MU-Analog-65-2L	MU-Analog-65	MU-Digital
Outputs	4–20 mA passive (2-wire)	4–20 mA · 0–20 mA · 0–10 V (all standard, active)	4–20 mA · 0–20 mA · 0–10 V (all standard, active)
Supply	11–30 V DC via the signal line (loop-powered)	24 VAC · 110 VAC · 230 VAC · 24 VDC (select at order)	24 VAC · 110 VAC · 230 VAC · 24 VDC (select at order)
Display	Analogue scale 150×150 mm	Analogue scale 150×150 mm	LCD, 3½-digit
Protection	IP65	IP65	IP54
Application	Retrofit and installations with simple 2-core wiring	BMS and SCADA integration with a scale readable without power	Standard transmitter for cleanroom, ventilation and HVAC

All three devices: measuring spans from 40 Pa (all combinations between ±20 Pa and ±1,800 Pa), max. error ±1.5 % FS (> 100 Pa) or ±1.5 Pa (< 100 Pa), factory calibration included in delivery.

Sizing: what to specify before ordering

Measuring range, display unit and supply are specified at order and set at the factory. Four points settle the sizing:

Measuring range

All combinations between ±20 Pa and ±1,800 Pa, smallest span 40 Pa. The span also determines the signal behaviour: small spans with mechanical low-pass damping, large spans with short response times.

Display unit

Specified at order and set at the factory — as a scale graduation (analogue) or display unit (LCD).

Supply and output

2-wire loop-powered (11–30 V DC, 4–20 mA only) or active with selectable supply voltage and all three outputs.

Factory calibration

Included in delivery for all three devices — every unit leaves the factory calibrated to the ordered measuring range.

Check the loop load (4–20 mA)

Maximum 600 Ω loop resistance at 24 V DC, including cable. Worked example: 100 m of copper cable (two cores of 0.5 mm²) gives around 7 Ω wire resistance, plus 250 Ω for a typical PLC input = 257 Ω — leaving around 340 Ω reserve for longer cables or daisy chains. At lower supply voltages the permissible load decreases; we calculate the loop budget individually on request.

Pressure tap inside the room: the RDS room pressure probe routes the measuring point through the wall with no electrical components inside the room — tool-free installation, compatible with all Rixen devices via the 8 mm nozzles.

View RDS

Typical applications

Cleanroom pressure cascade

Modern cleanroom wiring typically arrives 2-core at the field boxes — the MU-Analog-65-2L delivers the 4–20 mA signal directly to the GMP logging software, while the mechanical scale serves on-site personnel. Calibration histories typically show no deviations — the basis for significantly extended intervals under ISO 9001 and GMP Annex 1.

Industry: Cleanroom Industry: Pharma & GMP

Ventilation and filter monitoring

The MU-Digital is Rixen's standard transmitter for cleanroom, ventilation and HVAC. At small measuring spans, the sealing liquid acts as a mechanical low-pass filter — the output signal stays steady without damping parameters in the controller.

Industry: Ventilation

Furnace and thermal process engineering

For furnace pressure control, the Rixotact 4 combines a transmitter output (0–10 V) and a three-point step controller in one device — proven for decades in industrial furnace and thermal process engineering. If the signal runs to the plant control system, the MU-Analog-65 is the choice.

Industry: Furnace engineering

Related devices with transmitter output

RW65_EX_II

For hazardous areas: the MU-Analog-65, MU-Analog-65-2L and MU-Digital have no ATEX certification. The RW65_EX_II is certified intrinsically safe (II 1 GD Ex ia IIC/IIIC T4 Ga Da) and delivers 4–20 mA passive via a 2-wire transmitter — approved for Zones 0/1/2 and 20/21/22, connected via an isolation stage on the safe side.

View product

Rixotact 4

Differential pressure controller with a 0–10 V transmitter output and an integrated three-point step controller (relays open/close/hold) — for furnace pressure control and active room pressure hold.

View product

Frequently asked questions

Which transmitter fits your application?

Measuring span, supply, loop load, display — we support the selection and sizing of our transmitters directly. Send us the key data of your application.

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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.