How to Choose an Inclinometer for Machine Alignment

Four questions decide the sensor

Alignment questions arrive in a predictable order: how far can this axis drift, how tightly do I need to know it, what can I bolt to the machine, and what will the cabinet accept. Range, accuracy, mounting and output map onto a short list of families. Everything below uses ASM’s POSITILT line as the worked example.

1. Range: measure the fault, not the datasheet ceiling

The most common specification error is buying the widest range available. Range and accuracy trade against each other inside a family, because the MEMS element and signal chain are scaled across the span. ASM publishes POSITILT PTK6 static linearity at three angles, and the shape of that curve is the whole argument: 0.05° at ±30°, 0.1° at ±60°, 0.2° at ±180°. Same sensor, one quarter of the precision at the far end.

So start from the motion. A machine bed or surface plate that has drifted is a fraction of a degree out — you are hunting hundredths. That is a ±15° or ±30° window, and you should buy that window and enjoy the tighter linearity it carries. ASM builds POSITILT across ±15° to ±180° selectable ranges so this choice exists. Two axes cost range as well: the PTK6 covers ±180° on one axis but ±60° on two.

2. Accuracy: separate resolution from linearity

Vendors quote two numbers and buyers treat them as one. Resolution is the smallest step the sensor can report; linearity is how far the reported angle may stray from the true angle across the span. A sensor with 0.001° resolution and 0.2° linearity is not a 0.001° instrument, it is a 0.2° instrument with a fine display. The PTM27 offers resolution up to 0.001°, but that figure belongs to its narrowest range — at ±180° linearity is still 0.2°. Linearity is what enters your tolerance stack, so it is the number to negotiate.

Temperature is the other half of accuracy. The PTK6 is rated ±0.2° stability over −20…+40°C and ±0.4° over −40…+85°C. On a machine that starts cold and runs warm, the sensor itself moves half a degree across a shift — potentially more than the misalignment you are measuring.

Dynamic conditions are their own category. A standard inclinometer converts gravity into an angle, so acceleration along a measuring axis is indistinguishable from tilt; a vehicle that brakes reports an angle that is not there. ASM states the PTK line gives correct results under shock, vibration and acceleration — a requirement for moving equipment, not a refinement.

3. Mounting: three families, three mechanical realities

Alignment sensors divide by how they touch the machine, and the mechanics are unforgiving — a sensor bolted to a bracket that flexes measures the bracket.

Mechanical details are where installations fail. M4 screws into plastic strip if you torque them like a stainless body; the stainless versions take M6 or M8 and carry real preload. The PTK6 is potted and hermetically sealed, uses an M12 connector, and is specified to 100 g / 11 ms shock over 100 shocks and 20 g from 10 Hz to 2 kHz. It weighs about 390 g, so it will not measure the vibration of its own bracket. Housing material is EN 1.4404 (AISI 316L).

Two rules apply regardless of family: mount on the stiffest surface with the shortest bracket run, keep the sensor off thin panels that ring, and check the measuring axis against the tilt you actually care about.

4. Output: pick what your cabinet already speaks

Output is decided by the control system, not the sensor, so establish it before you shortlist models. ASM covers the common cases across POSITILT with voltage, current and CAN interfaces.

Note the current loop is three-wire, not the two-wire loop you may know from pressure transmitters, so confirm the card you are wiring into. On the CANopen version ASM lists a configurable 120 Ω termination resistor — check it is disabled if the sensor sits mid-bus. Measuring rate is 0.5 kHz on the PTK6 and 1 kHz on the analog variants, far faster than static alignment needs.

Which one to buy

PTM27 when you are levelling a machine bed, rail or plate and want the tightest linearity in a compact plastic housing — single or dual axis, IP67, resolution down to 0.001° at its narrowest range.

PTAM / PTDM stainless families when the machine lives in washdown, outdoors, in a hygiene zone or on a heavy vibrating frame — M6/M8 mounting, IP67/IP69, IP68 optional.

PTK6 or PTK29 when the sensor will measure a machine that is itself moving: a vehicle, boom, platform or crawler. You are buying the gyro compensation, the hermetically sealed housing and the 100 g shock rating.

Do not buy a wide-range sensor to gain margin: wide range costs linearity and the fault you are chasing is almost always small. Do not put a standard inclinometer on moving equipment — gravity versus acceleration is physics, not mounting.

Scenario picks

Where to buy genuine POSITILT inclinometers

Ruilianxin Technology supplies genuine ASM POSITILT inclination sensors — PTM, PTAM, PTDM and PTK families — sourced through authorised channels with original packaging and traceable documentation. If you are still choosing, send the measuring range, the number of axes, the mounting surface and the interface your cabinet uses, and we will come back with the family and the part number. Single-piece orders for maintenance and retrofit are normal for us. If your machine moves rather than sits still, say so in the first message — it changes the answer.

FAQ

Q1. Do I need a single-axis or dual-axis inclinometer for machine alignment?

Single axis, unless the machine tilts in two directions at once. Levelling a bed, rail or plate is a one-plane problem, and a single-axis sensor gives the full ±180° range with the simplest wiring. Choose dual axis for booms, platforms and vehicle frames — and note that using both axes costs range: the PTK6 delivers ±180° on one axis but ±60° on two.

Q2. What accuracy can I realistically expect on a machine-mounted inclinometer?

Better than most installations can hold. The PTK6 is linear to 0.05° at ±30° and 0.2° at ±180°, but its temperature stability is ±0.2° from −20 to +40°C. On a machine that warms up during a shift, the sensor’s own drift can exceed the misalignment you are chasing.

Q3. When is a gyro-compensated inclinometer necessary?

Whenever the sensor moves while it measures. A conventional inclinometer converts gravity to angle, so acceleration along a measuring axis reads as tilt — a braking vehicle produces an angle that is not physically there. Gyro-compensated units such as the PTK series are specified for vehicles, cranes and platforms rather than surface plates.

Q4. Which output signal should I specify?

Whatever your cabinet already accepts. Voltage (0.5…4.5 V or 0…10 V) suits short runs and simple analog inputs; 4…20 mA suits long runs in noisy plants, but the POSITILT current version is three-wire, not a two-wire loop. CANopen (CiA 301 / CiA 410) or SAE J1939 suits multi-sensor networks.

Q5. How do I mount an inclinometer so it does not lose accuracy?

Mount to the stiffest surface with the shortest bracket run, and keep it off thin panels that resonate. Match the fastener to the housing: M4 into plastic such as the PTM27, M6 or M8 into stainless PTAM5/6/7. For high-vibration machines choose a potted, hermetically sealed body — the PTK6 is rated 100 g / 11 ms shock and 20 g from 10 Hz to 2 kHz.

Related reading

• ASM POSITILT inclination sensors and the full ASM range: ASM brand overview
• All the industrial brands we supply: Brands
• Angle, displacement and inclination sensors by category: Products
• More selection guides: Knowledge Base
• Sensor mounting and measurement principles: Vibration Monitoring 101: sensor types and mounting
• Need a part number or a selection check: Contact us