User Manual

Tachometer wiring
Advanced Digital Motor Controller User Manual 149
Tachometer wiring
The tachometer must be wired so that it creates a voltage at the controller’s analog input
that is proportional to rotation speed: 0V at full reverse, +5V at full forward, and 0 when
stopped.
Connecting the tachometer to the controller is as simple as shown in the diagram below.
20kOhm
33kOhm
1kOhm
Max Speed Adjust
10kOhm pot
Zero Adjust
100 Ohm pot
1kOhm
Internal Resistors
and Converter
5V Out
Ground
A/D
Ta ch
Ana In
FIGURE 10-4. Tachometer wiring diagram
Brushless Hall Sensors as Speed Sensors
On brushless motor controllers, the Hall Sensors and most other types of rotor position
sensors that are used to switch power around the motor windings, can also used to mea-
sure speed and distance traveled.
Speed is evaluated by measuring the time between the transition of the Hall Sensors. A
32 bit up/down counter is also updated at each Hall Sensor transition.
Speed information picked up from the Hall Sensors can be used for closed loop speed op-
eration without any additional hardware on both sinusoidal and trapezoidal commutation.
Likewise, the position counter that is updated at every Hall transition can also be used to
operate the motor in Speed Position mode.
Speed Sensor and Motor Polarity
The tachometer, encoder or brushless sensor (Hall, Sin/Cos, SPI) polarity (i.e. which rota-
tion direction produces positive or negative speed information) is related to the motor’s
rotation speed and the direction the motor turns when power is applied to it.
In the Closed Loop Speed mode, the controller compares the actual speed, as measured
by the sensor, to the desired speed. If the motor is not at the desired speed and direction,
the controller will apply power to the motor so that it turns faster or slower, until reached.