Cost of Ownership: Comparing Tacho Generators to Hall-Effect and Optical Speed Sensors Over 10 Years
Speed feedback devices seldom fail outright—but when they do, the real price tag is usually hidden in production losses, rush-order parts, or frantic engineering hours. To help maintenance planners make a data-driven choice, we’ve modelled the full ten-year cost of three common sensor types serving the same 15-kW industrial drive:
| Cost Driver (10 yrs) | Brushless Tacho Generator | Hall-Effect Sensor | Optical Encoder |
|---|---|---|---|
| Purchase & install | £480 | £220 | £310 |
| Scheduled service (brush change, cleaning, calibration, etc.) |
£450 | £180 | £380 |
| Unplanned failures (mean-time-between-failure × downtime @ £900/hr) |
£900 | £1 530 | £2 700 |
| Spare parts & replacements | £300 | £380 | £600 |
| Energy draw (sensor + signal conditioning) |
£75 | £30 | £45 |
| Total 10-yr ownership | £2 205 | £2 340 | £4 035 |
Assumptions: 2 000 h/yr duty, clean but humid environment, single-shift maintenance crew; figures use mid-2025 UK averages for labour and energy. Actual values will differ, but the ratios hold surprisingly steady across many plants.
1 | Up-Front Spend
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Tacho generators cost more than a simple solid-state Hall device because they contain precision bearings, magnets, and wound stators.
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Optical encoders sit in the middle on price—but add installation complexity (shielded cable, alignment jig).
2 | Scheduled Maintenance
| Sensor | Typical Intervals | Cost Notes |
|---|---|---|
| Tacho (brushless) | Inspect bearings every 18 months; analogue calibration every 12 months | No brushes to swap, but still mechanical. |
| Hall-Effect | Visual check & connector reseat annually | Conformal coating prevents corrosion. |
| Optical | Clean glass disk & reseal every 6 months | Dust film = missed counts; more labour. |
Brushless tachos have closed housings, so servicing is mostly “look and listen.” Optical heads need regular lens wipes, especially in food, paper, or wood-dust zones.
3 | Unplanned Failures
Failure modes tell the real story:
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Tacho generator: Bearing seizure or demagnetisation—rare; vibration monitoring catches early.
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Hall-Effect: Wire fatigue or electronics spike—moderate; but swap-out is quick.
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Optical encoder: Light-path blockage, LED fade, or disk fracture—most frequent; each trip can snowball into hours of line stoppage while recalibrating zero position.
Our 10-year downtime estimate uses industry failure-rate data:
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Tacho MTBF ≈ 60 000 h
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Hall ≈ 40 000 h
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Optical ≈ 25 000 h
4 | Spare-Parts Pipeline
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Tacho: Only common part is a bearing kit; stocking one unit covers multiple motors due to standardised shaft sizes.
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Hall: Entire sensor is potted—failures mean full replacement.
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Optical: Each model has unique resolution & shaft hub—plants often stock two spares per motor size.
5 | Energy & Signal Conditioning
While all three sip milliwatts, the analogue signal conditioner for a tacho draws slightly more than a basic digital counter. Over a decade, the difference is lunch-money small—yet it’s sometimes cited in green audits.
6 | Intangible Factors (The “Soft Costs”)
| Factor | Tacho | Hall | Optical |
|---|---|---|---|
| EMI resilience | Excellent | Good | Fair |
| VFD plug-and-play | Analogue scaling only; trivial | Native pulses; fine | Needs high-speed counter |
| Speed bandwidth | Up to 10 kHz loops | Up to 5 kHz | 100 kHz+, but limited by contamination |
| Retrofit fit | Drop-in for legacy drives | Needs RPM-to-pulse converter | Often re-engineer control code |
7 | What the Numbers Tell Us
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Tacho generators edge out Hall sensors on total ownership by roughly 6 %. Their higher purchase cost is offset by fewer failures and modest service tasks.
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Hall-Effect sensors shine in lightweight, low-consequence machines where an extra outage hour won’t kill a shift OEE target.
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Optical encoders justify their premium only when micron-level position accuracy or multi-turn counting is essential—and the environment can stay clean. Otherwise, they are the most expensive path over a decade.
Conclusion: Choose by Risk, Not Sticker Price
If a single unplanned stop can wipe out days of profit, the steady analogue reliability of a tacho generator almost always wins the cost-of-ownership game. For lower-criticality assets, Hall-Effect sensors may keep CAPEX tidy. Optical encoders deliver unmatched precision—but be ready to pay in maintenance hours and spares.
Next step: Want a deeper dive using your plant’s actual labour rates and downtime costs? Send us your numbers, and we’ll run a custom 10-year model so you can invest with confidence.