Measuring the brake output voltage

The brake voltage is a square wave signal 16 kHz, 32 kHz or 64 kHz (configurable in subitem 2004:11). A PWM method is used for applying the appropriate voltage to the break output.

The break output voltage does not have a negative component. It is connected to an inductor which results in a constant current.

../../../_images/brake_voltage_measuring.png

Example

V in (Input DC voltage) = 48 V DC

Brake switching frequency = 16 KHz

Brake hold voltage = 24 V

Brake resistance = 50 Ω

T = \frac {1} {Brake~ switching~ frequency}  = \frac {1} {16000}

T_{on} = \frac {Brake~ hold~ voltage} {V_{in}} \cdot T   = \frac {48 V} {24 V} \cdot T = 0.5 \cdot T

Brake~ power = \frac {Brake~ hold~ voltage^2} {Brake~ resistance} = \frac {24^2 V} {50~ \Omega}  = 11.5 W

Attention

Applying more voltage to the brake than required will increase the brake temperature and damage the brake.

Danger

If the brake overheats while it’s released, the internal deformations might block the brake in the release state!

Measuring the brake current can be done with a DC ampere meter and measuring the brake DC voltage is possible with a common DC voltmeter.

Non-safety brake output

The image below shows a non-safety brake circuit. Measuring the non-safety break voltage can be done by connecting the voltmeter probe to the brake output (phase D on SOMANET Node) and ground.

../../../_images/non_safe_brake_voltage_measuring.png

Note

The brake or a similar electrical load has to be connected to the brake outputs when measuring the output voltage. Without a load, the multimeter will show the input DC voltage that is not correct!

Safety brake output

The image below shows the safety brake circuit. The PWM signal is connected to a switch that is connected to Ground (GND). So for controlling the voltage level, it is generating a PWM signal on the GND side.

../../../_images/safety_brake_voltage_measuring.png

For measuring the safety brake output voltage, B+ and B- should be connected to the voltmeter. Measuring the voltage between B+ and GND or B- and +V In will result in a wrong value.

Note

The brake or a similar electrical load has to be connected to the brake outputs when measuring the output voltage. Without a load, the multimeter will show an incorrect input DC voltage.