Routine calibration is the simplest way to ensure the speed-feedback voltage from your tacho generator matches the machine’s actual revolutions per minute (RPM). Keep loops tight, product quality high, and downtime low by following the clear steps below—no special software or programming required.

1. Prepare Safely and Set Up

• Isolate all drives with lock-out/tag-out before you touch the shaft.

• Clean the commutator (for brushed models) so dust or glaze won’t distort readings.

• Let the unit reach room temperature; large swings affect magnets and coil resistance.

• Use traceable instruments: a certified laser or optical tachometer for true RPM and a true-RMS digital meter for accurate voltage.

• Give the generator ten minutes at low speed if you’re in a damp area—warmth drives off condensation.

2. Know the Target Voltage Constant

Every tacho generator has a rating plate that tells you its voltage constant (often written as “10 volts per 1,000 rpm” with a small tolerance). Your job is to make sure the measured voltage stays within that tolerance at any given speed.

3. Confirm Mechanical Alignment

1. Check shaft run-out; anything more than a hair’s breadth of wobble stresses bearings and hides electrical errors.

2. Verify a flexible coupling is installed so thermal growth can’t bend the rotor.

3. Lightly pull on the shaft—small axial float is normal, sideways play is not.

4. Record a Baseline Reading

1. Bring the motor to half its rated speed.

2. Note the RPM on your handheld tachometer.

3. Measure the generator’s output voltage with your meter.

4. Divide the voltage by the thousands of RPM to see whether it equals the nameplate constant. If the error is within one percent of full-scale, you’re finished—log it and move on.

5. Adjust If Needed

Modern drives often have a simple gain or scaling parameter. Increase or decrease that setting until the displayed speed matches the handheld tachometer reading.

Older analogue converters usually feature a small trim potentiometer. While the machine runs at about 80 percent of top speed, turn the pot slowly until the meter shows the correct voltage. Lock the setting with a dab of non-conductive varnish.

Never dismantle the generator to “tweak” the magnets; field adjustment risks permanent damage.

6. Verify Linearity at Several Speeds

Repeat the check at roughly ten, fifty, and one-hundred percent of maximum RPM. The voltage at each point should stay within half a percent (or whatever your site standard demands). If it does, the unit passes.

7. Check for Ripple and Electrical Noise

A quick look with an oscilloscope—set to AC coupling—will show any unwanted ripple on the DC output. Excessive ripple usually points to worn brushes, rough bearings, or a bent shaft. Fix the mechanical issue, not the electronics.

8. Seal and Secure Everything

Tighten terminal screws, replace gaskets, and add a small seal over adjustment pots so they can’t drift or be disturbed accidentally.

9. Document the Result

• Fill out a calibration sheet with date, instrument serial numbers, and your three-point data.

• Update the asset register with the new voltage constant and next due date.

• Affix a simple “CAL OK” tag on the terminal box.

Good records make audits painless and prove compliance with quality systems like ISO 9001.

10. Choose the Right Interval

• Standard industrial duty: once a year or every 8,000 operating hours.

• High-precision servo loops: every six months.

• Harsh or wash-down environments: brief spot checks each quarter.

Final Word

Calibrating a tacho generator takes less than an hour and pays off in consistent product quality and stable process control. Follow the steps above, log your work carefully, and your generator will deliver accurate speed feedback for many trouble-free years