When Is A Tachometer Required - Allen-Bradley PowerFlex 7000 User Manual

B-4 Catalog Number Explanation – Drive Selection
When is a tachometer When is a tachometer
required?
required?
7000A-UM151E-EN-P - October 2018
A tachometer is required under the following conditions:
1. When speed regulation accuracy must be between 0.01 – 0.02%
of nominal speed.
2. When the zero speed breakaway torque needed is greater than
90% of continuous running torque.
3. When continuous running speed is greater than or equal to 0.1
Hz, but less than 6 Hz.
4. For minimizing restart times using the flying start capability in
forward or reverse direction.
Table B-2 –Power Flex Speed Regulation
Tachometer
Without Tachometer Not applicable
With Tachometer
Notes:
Speed Regulation is based on % of motor synchronous speed.

Tachometer to be mounted on the AC machine

Operational 15 V DC Power Supply mounted in drive to power

the tachometer as a standard option with the tachometer feed
back card.
Customer is responsible for providing and mounting of

tachometer
Sleeve bearing motors require the tachometer to have an axial

movement tolerance.
Recommended tachometers are the shaft mounting type,

examples are the Avtron 585 and 685 models or the Northstar
(Lakeshore) RIM Tach HS85, 12 to 15V models or equivalent.
Magneto resistive models are more adaptable to harsh
environments.
When installing, the tachometer body and electronics must be

isolated from ground (options available from the tachometer
manufacturer to accomplish this).
When cable lengths exceed 305 m (1000 ft.) for the Northstar or

610 m (2000 ft.) for the Avtron, consult the factory.
Table B-3 – Tachometer Selection
Recommended Tach PPR
Motor RPM
3600
3000
1800
1500
1200
1000
900
720
600
Frequency Output
< 6 Hertz 6 – 15 Hertz
0.1 %
0.02 % 0.01%
Tach ppr
600
600
1024
1024
2048
2048
2048
2048
2048
Above 15 Hertz
0.1 %
0.01%
7000 "A" Frame