AXILINEHow to Choose a Balancing Instrument: Vibrometer, Analyzer or Balancer
You've been given a budget for “a vibration instrument,” and that's where the clarity ends. One quote is for a pocket vibrometer at a modest price, another for an eight-channel analyzer, a third for a balancing kit in a case. All three vendors promise to solve your problem. Below we go through what actually separates the instrument classes, which datasheet lines to check, and when you don't need to buy anything at all.
Four instrument classes: what each one can and can't do
The market calls almost anything that displays mm/s a vibrometer, an analyzer or a balancer. The difference between the classes isn't price and isn't the number of buttons. It comes down to two things: whether the instrument has a phase-sensor input, and whether the software can calculate a correction weight. Everything else is secondary.
Sort instruments into four groups. Within a group, models differ in details; between groups, they solve different problems and don't substitute for one another.
1. Vibrometer: one number
Displays overall RMS vibration velocity in mm/s (RMS — root-mean-square value), usually on a single channel. Good for walking a route through the shop, recording numbers at the same points, comparing them against setpoints, and watching a trend. Not suited to balancing: a single amplitude without phase doesn't tell you where the heavy spot sits. The reverse also holds: any balancer can work as a vibrometer, and on the Balanset-1A the Vibrometer mode works even with the phase sensor disconnected — you're just left with a single overall RMS reading on screen. That's exactly what a standalone vibrometer gives you.
2. Vibration analyzer: spectrum and signal
Computes an FFT spectrum (vibration broken down by frequency), shows the time waveform, and often provides an acceleration envelope (a method for pulling weak impacts from a defective bearing out of the overall signal) and a bump test — an impact check of natural frequencies. It's what answers the question “why is it shaking”: does 1x dominate (vibration at running speed — the signature of unbalance), does a 2x show up, are harmonics or high-frequency bearing peaks appearing. It can only balance under two conditions: it has a tachometer input, and the software has a balancing module. An analyzer without those two things diagnoses, but won't calculate a correction.
3. Balancing instrument: calculates the weight
Two vibration channels plus a laser phase sensor with a reflective marker on the shaft, and software that calculates the correction using influence coefficients — numbers that show how a weight in each plane changes the vibration at the supports. The instrument measures the amplitude and phase of the running-speed component, learns from the trial weight, and outputs a mass and angle, or a blade number. This is the only class that covers two-plane balancing in a machine's own bearings.
4. Permanent monitoring system
Sensors stay on the machine permanently, a cabinet collects data around the clock, and warning and alarm setpoints trigger without a person involved. The purpose is different: not to take a single reading, but to not miss degradation. Balancing off this system is awkward, and often impossible, because the sensor locations and recording regimes are chosen for monitoring, not for trial runs.
Check just two lines on the datasheet: whether there's an input for a phase sensor (tachometer), and whether the software description says “correction weight calculation.” If even one is missing, what you have is a meter, not a balancer, no matter what it costs.
Sources: Balanset-1A operation manual · Balanset-1A manufacturer specification
Table: which task needs which instrument
Read the table from the right-hand column. If the item you need isn't in the package, the instrument won't solve the task, and a software update won't change that.
| Task | Minimum sufficient class | What must be included |
|---|---|---|
| Route walk, trending | Vibrometer | RMS vibration velocity, the same points and measurement direction every time |
| Condition assessment by zones A–D (from A “like new” to D “unacceptable”) | Vibrometer with a suitable band | RMS over the 10–1000 Hz band per the applicable part of ISO 20816 |
| Working out whether it's unbalance or not | Vibration analyzer | FFT spectrum, comparing overall vibration against 1x |
| Bearing diagnostics | Vibration analyzer | Acceleration channel, high frequencies, envelope |
| Checking for resonance | Analyzer or balancer with coast-down recording | 1x amplitude and phase during run-up or coast-down |
| Single-plane balancing of a disc | Balancer or analyzer with a balancing module | One vibration channel, phase sensor, correction calculation |
| Two-plane rotor balancing | Two-channel balancer | Two channels with simultaneous acquisition, phase sensor |
| Batch balancing on a machine | Measuring core for a rig | The same two channels and phase, sensors permanently mounted |
| Round-the-clock monitoring of a critical machine | Permanent system | Permanent sensors, setpoints, archive and alerting |
Honestly, about one row in the table. A balancing instrument does show a spectrum, but per the manual, the Balanset-1A's RMS vibration velocity measurement band is 5–200 Hz. That's enough for the running-speed component of almost any industrial machine, and not enough for bearing defects, which live at high frequencies. If you specifically need bearing diagnostics, get an analyzer with an acceleration channel and envelope processing.
Sources: Balanset-1A operation manual · ISO 20816-1:2016
Why two channels and a phase sensor aren't a luxury
Two-plane balancing solves a system of two equations. A weight in the first plane changes the vibration not only at its own support, but at the second one too, and vice versa. The instrument describes this with four influence coefficients, each with its own amplitude and phase. To calculate them, you need to know the state of both supports at the same instant, in the same run.
Now picture a single-channel instrument. You measure the first support, stop the machine, move the sensor, spin it up again, measure the second. In that time the speed has drifted a little, the bearings have warmed up, the damper has settled slightly differently. You'll get similar amplitudes, but the phase relationships between the supports will already have shifted. The software will then honestly calculate a correction from data taken from two different states of the machine, and you'll be left wondering why the check run doesn't match the calculation.
Two-channel acquisition removes this problem entirely. Both accelerometers record simultaneously and are referenced to the same tachometer pulse, so the phases at both supports are comparable by definition. For two planes you make three runs: an initial one, plus one trial run per plane.
The phase sensor is its own story. It's what pulls the running-speed component out of the overall vibration and sets the reference point for the angle. Without it you have neither 1x nor phase — only an overall number. Balancing methods without a tachometer do exist, for instance moving the trial weight through marked positions and building the solution from amplitudes. They work, but going without a tachometer costs you extra runs and marking. On a site visit, where every run means coordinating with the operator plus a run-up and a coast-down, that trade isn't worth it.
A single-channel balancer remains a workable tool for disc-shaped rotors, where one plane and one support settle the matter. As soon as the rotor is elongated and couple unbalance appears (unbalanced masses at the rotor's ends are turned against each other and rock it through a tilt), the second channel stops being a convenience and becomes a condition for repeatability.
Sources: Balanset-1A operation manual
Hardware: what to check on the datasheet
It helps to read the datasheet lines against your own machines, not in isolation. Take the slowest unit in your shop and the fastest spindle, look at their speeds and at where the sensor will physically go. Then compare. In the right-hand column we give the Balanset-1A's figures from the manual as a reference point, something to check other datasheets against.
- Mounting. Put the magnet on a clean, flat pad, free of paint buildup and rust. An M4 stud gives a more honest signal at high frequencies, but needs a threaded hole in the support. Keep the measurement direction the same from one reading to the next, usually horizontal-radial.
- Sensor sensitivity. The standard accelerometers run around 20–30 mV/(mm/s), and the whole signal path — preamplifiers, integrators and ADC — is matched to them specifically. The coefficient is entered in the settings window and only changes when you swap the sensor. Don't assume an arbitrary third-party accelerometer will drop into someone else's instrument without checking.
- Cables. Ask about the length of the standard cables and whether they're sold separately. A cut sensor cable is the most common field failure, and it's good when it's replaceable as a consumable, not along with the module.
- Computer. The software runs under Windows, the module is powered over USB. A tablet on a different system won't work. When the mains supply is poor, the manual directly recommends running from the laptop's battery.
| Parameter | Why it matters | Balanset-1A as a reference |
|---|---|---|
| Vibration channels | Two planes require simultaneous acquisition at two supports | 2 channels, inputs X1 and X2 |
| Phase sensor | Without it there's neither 1x nor a weight-placement angle | Laser tachometer, input X3, reflective marker on the shaft |
| 1x RMS vibration velocity range | Must cover both an in-tolerance machine and an alarm one | 0.02–80 mm/s |
| RMS measurement band | Check whether your rotational frequency falls inside the band | 5–200 Hz |
| Speed range | Slow-running mixers and spindles sit at opposite ends | 100–100,000 rpm |
| Phase error | A phase error turns into a weight-angle error | ±1° |
| Number of correction planes | You can't finish an elongated rotor without two planes | 1 or 2 |
| Sensor mounting | A magnet is faster, a stud is more honest at high frequencies | Magnets or M4 studs |
| Sensor size and mass | A large sensor won't fit into a tight bearing support | up to 25×25×20 mm, up to 40 g |
| Kit weight | One person will be carrying it, including up stairs | case 39×33×13 cm, under 5 kg |
| Power | In the field, an extra power supply means an extra socket you need | USB from the laptop, no separate supply needed |
| Operating conditions | A boiler house in summer and a shop in winter are different conditions | +5…+50 °C, humidity under 85% non-condensing |
Sources: Balanset-1A operation manual
Software: where the instrument saves you runs
The hardware on mid-range instruments is similar. In the field, the difference builds up from small things in the software, because every small thing turns into either a saved run or an extra hour on site. Here are the features worth looking for in the spec sheet and asking to see demonstrated.
Saved influence coefficients
Balance a machine once, save the coefficients, and a repeat balancing job of the same type then takes one run instead of two or three. The conditions are strict: mount the sensors and the marker the same way as the first time, keep the same speed, and enter the trial weight's mass in grams, not percent, during the first balancing job.
Trim balancing
After the check run, the software doesn't tell you to redo everything — it calculates a small top-up to add to the weights already fitted. This is what you'll use to bring the machine the rest of the way into tolerance. Without this feature, the job turns into trial and error.
Fixed positions and drilling
You set the actual mounting locations: blades, bolt holes, twelve holes at 30° spacing. The instrument outputs position numbers and masses split across the two nearest positions, not an angle. No protractor needed, and the mirror-image error in the direction of angle measurement disappears. If you're correcting by removing material, the software rotates the angle by 180° automatically.
A prompt on whether the trial weight is valid
The instrument tells you on its own whether the response changed enough. The rule of thumb is simple: the 1x amplitude should change by at least 20–30%, or the phase by at least 20–30°. The manual calls this the 30/30 rule. Without this prompt, an untrained operator will happily calculate a correction from readings that barely changed at all, and get garbage.
Tolerance calculation in g·mm
The software calculates the tolerance for residual unbalance by balance quality grades G (the lower the grade number, the tighter the tolerance). This is a separate quantity — don't confuse it with the target 1x in mm/s, or with a machine's condition assessment from overall vibration. Record the applicable part and edition of ISO 21940-11 separately if the result feeds into a contractual acceptance.
Archive and report
Every balancing job gets its own folder, holding a time-stamped log of runs, charts, and a report file that opens in the built-in editor and prints. If you're a repair contractor, the report is half of the deal with your client.
Polar diagram
A vector picture instead of a column of numbers. It shows at a glance where the vector moved after the trial weight and whether the process is converging toward the center. One look at the diagram often catches an error in the direction the angle is measured.
Recalculating to other planes, and the arbor
The weight is calculated for a plane you physically can't reach. The recalculation function transfers masses and angles to other planes based on entered distances and radii, which helps on complex-shaped rotors such as crankshafts. A separate option calculates arbor eccentricity (its own runout): the rotor is remounted on the arbor at 180° and an extra run is taken.
Manual entry and session recovery
Manual entry of amplitudes and phases lets you recalculate a correction from data taken with a different instrument. Session recovery saves you when the laptop freezes mid-balancing job and redoing the trial runs is the last thing you want to do.
Sources: Balanset-1A operation manual · ISO 21940-11:2016
Who's going to operate the instrument
This is the question people forget to ask before buying, and then the instrument sits in a cabinet. A balancer is designed for an operator with no specialized vibration training, and the Balanset-1A manual states this directly: the software walks you through the runs and calculates the solution itself. But it won't make the decision for you on whether to balance or fix the mechanics first.
It helps to look at the tasks through the lens of ISO 18436-2, which splits vibration specialists into categories. The match to instrument classes turns out to be almost word for word.
- Category I, data collector. Carries out simple single-channel measurements by a set procedure, compares one number against setpoints, reports deviations. Choosing the sensor and method, analysis and diagnostics aren't part of their tasks. A vibrometer is enough for this person.
- Category II, analyst. Takes single-channel measurements with a phase trigger, reads the spectrum, diagnoses typical defects, performs single-plane balancing and a simple bump test. This already needs an analyzer or a balancer.
- Category III, diagnostician. Specifies the instrument fleet, writes procedures, assesses setpoints, carries out two-plane balancing in the field. This is the level that chooses the instrument and works through disputed cases.
The practical takeaway. You can buy a two-channel balancer and put a Category I-level person on it, and they'll get results on simple fans in fixed-position mode. But when overall vibration turns out to be three times higher than 1x, they'll need someone to tell them “that's not unbalance, stop.” Build that person into the plan from the start: your own specialist, training, or the supplier's advisory support.
Buy an instrument, or book a site visit
Count the cost of the skill, not the cost of the instrument. You'll buy the instrument once, but the ability to tell unbalance apart from misalignment and resonance is only built through practice. If you'll be balancing twice a year, by the third time your technician will have forgotten which way to measure the angle.
- A middle option often turns out best. You buy the instrument and, at the same time, book a site visit for the first machine. An engineer arrives with their own kit, your technician stands alongside and does the first balancing job with their own hands. By the end of the day you have a balanced machine, a trained person, and a sample report.
- Count the cost of ownership more broadly than the price of the case. It includes a Windows laptop, reflective tape or replacement markers, magnets, correction weights and a way to attach them, operator time, software updates, and a spare sensor cable.
- Ask about repairability before you pay. Can the sensor be replaced on its own, the cable on its own, the measurement module on its own. How long a replacement sensor takes to arrive. Who answers calculation questions, and in what language.
- Before you work out the savings, answer one question: who on your shift is going to pick up that case on a Friday evening when the induced-draft fan goes down? If there's no answer, buying the instrument doesn't solve your problem.
| Your situation | What makes more sense | Why |
|---|---|---|
| One to three balancing jobs a year, non-critical machines | Book a site visit | The instrument will sit in a cabinet, and the skill won't build up |
| Balancing monthly, you have your own technician | Buy the instrument and train the person | Your own instrument removes waiting for a contractor from the repair schedule |
| Critical machine, downtime isn't acceptable | Your own instrument plus supplier support | A same-hour response matters more than the kit's price |
| Repair contractor, customers' rotors | Your own instrument, no question | You need reports and independence from someone else's schedule |
| First time, the cause of vibration is unclear | A diagnostic site visit first | Find the cause first, then decide what to buy |
| Batch balancing of identical rotors | Instrument plus a balancing rig | Saved influence coefficients give you one run per rotor |
When you need the instrument inside a rig, not in a case
A separate case: you don't need on-site balancing, you need batch balancing on a machine. Then you're not choosing a case, you're choosing a measuring core. The kit is essentially the same: two accelerometers on the machine's supports, a laser phase sensor on a bracket, a two-channel module and software on a computer in a cabinet. A magnetic stand and a carry case are unnecessary here; the sensors stay permanently mounted on the supports.
The Balanset-1A manual directly describes this application: the instrument works either for balancing in a machine's own bearings, or as the measuring system for soft-bearing, that is, above-resonance, balancing machines — theirs are compliant supports, with running speed above the supports' own natural frequency. Hence the restriction: the machine's supports must visibly oscillate under the action of unbalance, because accelerometers measure the movement of the support, not the force in a rigid connection.
Retrofitting an existing machine — see our separate write-up on retrofits: it covers reworking the supports, sensor mounting pads, the drive and metrology. Don't have a machine yet, but you have a lot of identical rotors — read our piece on building a balancing rig yourself.
Sources: Balanset-1A operation manual · Balanset-1A manufacturer specification
What to check before you pay
A demonstration in a meeting room on a tidy demo rotor will show you that the software works. It won't show you whether you can handle your own impeller in a tight housing. Go through this list before you transfer any money.
- A demonstration on your own machine, not a showroom rotor. Have them show the full cycle: initial run, trial weight, correction, check run.
- Training: who trains, how long it takes, what happens if the person changes.
- The software interface language and the manual's language. Check that it's a language your technician actually reads.
- Software updates: how they're released, whether they're paid, what happens to the license when you replace the laptop.
- The full delivery list in writing: sensors, cable lengths, magnetic stand, scale, reflective tape, case, software media.
- A sample report. Look at it through the eyes of your client or your own reliability department: is there enough data for acceptance.
- How the instrument calculates tolerance: only by a target 1x in mm/s, or also by residual unbalance in g·mm against G grades.
- The speed range and frequency band against your list of machines, including the slowest and the fastest.
- Lead time for a replacement sensor and cable, and who to call when the numbers don't add up.
We're engineers who design and manufacture the Balanset instruments and balance with them on site ourselves, so our advice is a practical order of operations. Start with a site visit to your specific problem machine. You'll get measurements, an answer to whether it's unbalance or misalignment, and you'll see the instrument working on your own equipment at the same time. After that, the purchase decision takes five minutes and doesn't rely on anyone's promises. If you need an instrument for a rig or for a run of identical rotors, send us your machine fleet and speeds, and we'll work through the fit before you order.
Sources: Balanset-1A manufacturer specification
Frequently asked questions
Can you balance a rotor with an ordinary vibrometer?
No, if by vibrometer you mean an instrument that gives one number for overall vibration. Calculating the correction needs the amplitude and phase of the running-speed component, and only a phase sensor with a marker on the shaft gives you phase. Tachometer-free methods do exist, where you move a trial weight through marked positions in sequence and build the solution from amplitudes alone. They work, but they need more runs, careful marking and patience, and on a running production line every extra run costs time. If balancing is regular work for you, get an instrument with a phase sensor.
Is a single-channel instrument enough for two-plane balancing?
Formally, a solution exists: you measure the supports one at a time, moving the sensor between them. In practice you double the number of runs and lose the correct phase relationships between the supports, because the machine has time to change between readings: the speed drifts, the bearings warm up, the flow regime shifts. The influence coefficients end up assembled from different states of the machine, and the check run stops matching the calculation. For a disc-shaped rotor with one plane, a single channel is acceptable; for an elongated rotor, get two.
Do I need a separate vibration analyzer if I buy a balancer?
It depends on what you're diagnosing. A balancer shows the time waveform, the spectrum, harmonic analysis, and overall vibration and 1x separately, and that's enough to decide whether balancing is appropriate and to spot misalignment or looseness. For bearing defects, that's not enough: they show up at high frequencies, and per the manual, the Balanset-1A's RMS vibration velocity measurement band is 5–200 Hz. If your reliability program is built around early detection of bearing defects, add an analyzer with an acceleration channel and envelope processing.
Will a tablet or smartphone work instead of a laptop?
No. The Balanset-1A software runs under Windows, and the measurement module is powered and transfers data over USB. A tablet on a different operating system won't work. Any laptop or panel PC with Windows and a working USB port will do. That's also an advantage in the field: when the mains supply is poor, the manual recommends running from the laptop's battery, so you don't depend on a socket next to the machine.
What's the difference between a field instrument and a system for a balancing machine?
The measurement core is the same: two accelerometers, a laser phase sensor, a two-channel module and the software. What differs is the surrounding setup. A field kit lives in a case, sensors go on magnets on the machine's bearing supports, and a magnetic stand holds the tachometer. On a rig, the sensors are permanently mounted on the supports, the tachometer sits on a bracket, the computer lives in a cabinet, and the delivery set is agreed for the specific design. There's one requirement for the machine: the supports must visibly oscillate, which is why soft-bearing, above-resonance machines are supported as standard.
How do I know an instrument won't suit my machines?
Check five things, and preferably before buying. The speed falls outside the 100–100,000 rpm range. There's no access to the bearing supports to mount a sensor close to the bearing. There's no access to the shaft for a reflective marker, and no other surface for one either. Overall vibration is several times higher than 1x, meaning the main source of vibration isn't unbalance, and balancing won't remove it. Contractual acceptance requires assessment over the 10–1000 Hz band per the applicable part of ISO 20816, and the instrument's RMS measurement band is different. Any one of these is a reason to take a trial reading first and decide afterward.
Related content
How to Choose a Balance Quality Grade: G6.3, G2.5, and Everything Else
Grade G per ISO 21940-11 (formerly ISO 1940-1) sets the allowable residual unbalance of the rotor itself, not the vibration level at the bearing housing. The number in the grade designation equals the product of the allowable specific residual unbalance and the angular velocity, expressed in mm/s: for G6.3, that product equals 6.3 mm/s. For most on-site work on fans, pumps, impellers, and general-purpose electric motors, the baseline choice is G6.3; G2.5 is used for high-speed machines, turbines, and machine-tool drives; G1.0 and G0.4 are reserved for precision spindles. At the same grade, the allowable mass falls in inverse proportion to speed: spin twice as fast, and half as many grams are allowed.
How to choose a balancing and vibration diagnostics contractor: questions, red flags, contract
Ask three things: what you measure with and how many channels, whether you measure phase and speed, and what you'll do if the cause isn't unbalance. A specialist will answer with a two-channel analyzer with a phase sensor keyed to a mark on the shaft, comparing overall vibration against the 1x running-speed component — the part of the vibration that repeats exactly once per shaft revolution — and that they won't balance if the 1x share is small. Someone with a plain vibrometer promises a result before the measurement and won't show you before-and-after data. A method's limits, stated out loud, are more reliable than any 'we'll fix everything' guarantee.
Conveyor Pulley Balancing: Drive, Take-Up, and Bend Pulleys
Yes, we balance conveyor pulleys on site, in their own bearing units, with weights on the end discs in two planes. An honest caveat: below roughly 120 rpm the forces from imbalance are negligible, and the running frequency drops toward the lower measurement limit. So we first check belt tension and tracking, lagging wear, buildup, the motor-gearbox unit, and the bearing units. Balancing is worthwhile on pulleys from ~120 rpm up, after a shell repair, when a factory weight has been lost, or when there's water or buildup inside the body.
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