Knowledge / Commissioning
Commissioning a ring balance
Complete guide for all Rixen ring balances — RW65, MU-Analog-65, MU-Digital, MU-Analog-65-2L, RW65_EX_II, Rixotact 4. Based on the factory operating manuals.
- · Spirit level (two-axis)
- · Crosshead and Allen key set
Important notices before commissioning
These notices apply to all models. Ignoring them can cause oil loss or permanent damage.
The device contains sealing oil. While the valves are open, the device must not be disassembled, tilted, or transported on its side — the oil will run out and the device must be returned to the factory for refilling. Always close valves (turn clockwise until stop) before removing the device from the wall.
The pointer sits on a delicate shaft. Mechanical force on the pointer bends it or causes it to slip on the shaft — both result in permanent reading errors. Pointer movement only via the locking screw A or by applied pressure.
For the oil level check (functional test), only blow gently into the left nozzle — up to full scale maximum. Compressed air or forceful blowing can flip the ring body and eject oil. Never create vacuum by sucking with your mouth.
Commissioning — step by step
Check delivery
Remove device from packaging. Delivery includes: device, factory calibration certificate (with device number).
Keep the calibration certificate and operating manual in a safe place.
Always have the device number (Instr. No.) ready when contacting us.
Open housing and mount device vertically
Align the device vertically on a flat, low-vibration wall. Use a spirit level — check on both axes. Deviations cause measurement errors: 1° of tilt produces 3° of pointer offset.
Tighten mounting screws. Use shims if needed to achieve exact vertical alignment. Zero correction screw N (eccentric) is for final fine-tuning only — not as compensation for a tilted installation.
The device must be mounted vertically only. If mounted at an angle, oil will leak out.
Open valves
Only now — after vertical mounting — turn both valves V counter-clockwise to their stop (open). Both must be fully open.
Partially open valves cause measurement errors and allow the medium to leak past the valve seat into the housing.
Open valves only after the device is correctly mounted. Open valves on an unmounted device → oil runs out.
Release transport lock
Turn locking screw A counter-clockwise to its stop. The ring body is now free to move.
The pointer should settle to zero on its own. For measuring ranges below 100 Pa this can take 2–3 minutes — be patient, do not assist.
The transport lock secures the ring body for transit and dismounting. A forgotten lock is the most common reason a device shows no response to pressure.
Zero correction
For zero check: both valves fully open, both nozzles pressure-free and open to atmosphere, device exactly vertical.
Devices with analogue scale (RW65, MU-Analog-65, MU-Analog-65-2L, RW65_EX_II, Rixotact 4): if the pointer is not at zero, fine-adjust with eccentric screw N. The screw has its greatest effect when the slot is turned 90° left or right. Allow the ring body to settle fully after each adjustment.
MU-Digital: correct the zero point electronically via the internal potentiometer — no mechanical screw N on this model.
Screw N (analogue models) and the potentiometer (MU-Digital) are for compensating installation-related offsets (tilt) only — not for correcting mechanical hysteresis. The factory calibration certificate shows two zero values: one approached from below and one from above (e.g. −0.2 Pa and +0.3 Pa). This difference is normal bearing friction, not a defect. Do not force the zero to exactly 0.0 Pa — this shifts the hysteresis onto the scale and increases the measurement error across the entire range. If adjustment is made: set to the midpoint of the hysteresis band as shown in the calibration certificate.
Connect pressure tubing
Left nozzle = p+ (higher pressure), right nozzle = p− (lower pressure). For differential pressure measurement connect both nozzles: p+ to the high-pressure measurement point, p− to the low-pressure measurement point. For gauge or vacuum measurement, leave p− open to atmosphere.
The nozzles are 8 mm in diameter. Process lines connect directly to them — flexible tubing or rigid piping both work, as long as the connection is leak-tight.
Swapped connections do not damage the device but invert the reading. Verify the assignment against the piping plan before connecting.
For vacuum (negative pressure) measurement: p+ (left) to the measurement point, p− (right) open to atmosphere — identical to positive pressure, the reading will simply be negative.
Connect electrically
Connect as per the wiring diagram supplied with the device. For model-specific terminal assignments refer to the operating manual included in the delivery.
Check zero point
Leave both nozzles open to atmosphere — both sides are then at the same pressure. Pointer or display must go to zero.
If an offset remains: re-check vertical alignment with spirit level. If the deviation after correction exceeds the accuracy limit (±1.5 Pa for ranges < 100 Pa; ±1.5 % FS for ranges > 100 Pa) → return device for factory inspection.
Start up the system
Connect pressure tubing to the process connections (p+ left, p− right). Check all connections for leaks.
Start the system and check whether the readings are plausible — i.e. whether the pointer or display is in the expected range.
On unexpected readings: check connections for leaks, verify vertical alignment, and repeat the zero check (step 08).
Close housing
Place cover accurately and tighten the screws evenly.
Functional check of the measuring element
Recommended after faults, extended standstill, or as a general check. Both tests can be performed without disassembly.
Check oil level
- 1.Attach a clean flexible tube to the left nozzle (p+).
- 2.Blow gently into the tube and observe the pointer.
- 3.Result OK: pointer rises to full scale — sufficient sealing fluid present.
- 4.Result NOK: air escapes from the right nozzle before full scale is reached → oil must be refilled (contact Rixen with device number).
Never blow harder than full scale — the ring body can flip over and eject oil.
Never create vacuum by sucking with your mouth. For the vacuum test: attach tube to right nozzle and blow gently — inverted pressure simulates vacuum.
Check mechanical zero
- 1.Both valves fully open, both nozzles pressure-free and open to atmosphere.
- 2.Check vertical alignment with spirit level.
- 3.Pointer must go to zero. For ranges < 100 Pa: allow 2–3 minutes.
- 4.Fine-adjust: analogue models (RW65, MU-Analog-65, MU-Analog-65-2L, RW65_EX_II, Rixotact 4) via eccentric screw N. MU-Digital: correct zero point via the internal potentiometer. Allow ring to settle fully after each adjustment.
The measuring element operates maintenance-free and wear-free under normal conditions. If the pointer does not go to zero after correct alignment and N-adjustment → contact Rixen (bearing friction or swollen internal silicone tubes from oil ingress; both rare).
Decommissioning
- 1.Switch off supply voltage (if transmitter present).
- 2.Remove cover. Disconnect electrical cables.
- 3.Carefully move pointer (hold near the shaft only, never pull on the pointer blade!) to locking position P.
- 4.Turn locking screw A clockwise to stop — measuring element is now secured.
- 5.Close both valves V (turn clockwise to stop).
- 6.Replace cover. Remove device from wall.
Common issues
Pointer / display does not go to zero
- Device not exactly vertical — check with spirit level, realign
- Locking screw A still tightened — turn A counter-clockwise to stop
- Nozzles not pressure-free — for zero test, open both nozzles to atmosphere
- Vibration from nearby equipment — change location or isolate
No response to applied pressure
- Locking screw A not released — most common cause
- Valve(s) not fully open
- Leaking or kinked tubing connection
- Pressure ports swapped — pointer deflects in opposite direction
4–20 mA signal out of tolerance
- Loop resistance too high — at 24 V DC max. 600 Ω (MU-2L); check datasheet for others
- Supply voltage wrong or unstable
- ATEX: Zener barrier parameters do not match Ui of device
Display noisy or pulsating
- Process pressure fluctuations — normal for small spans (< 40 Pa)
- Tubing too short — insufficient damping volume
- Tubing pinched or sharply bent — check routing
Zero drifts after weeks
- Building settlement or maintenance changed alignment — check with spirit level
- Tubing leak — almost always the cause when alignment is correct
- Mechanical drift of measuring element: physically excluded
Frequently asked questions
Questions about commissioning?
For special configurations, ATEX sizing, or if the device is not behaving as expected — we help directly. Please have the device number (Instr. No. on the nameplate) ready.