What measures must be taken to build up a EMC consistent installation (CE)?
The term „Safety earth“ is defined as a security measure for the protection of people. The term „Shielding earth“ includes the connection points where cable shields are connected. As a rule the safety earth and the shielding earth have the same potential.
While the connection of a machine to the safety earth guarantees the protection against overvoltage in the case of an error, the connection of the cable shields to the shielding earth represents a protection against interference immission and emission.
For maximum interference suppression the cable shields must be mounted on both ends and with a resistance as low as possible. Exceptions need a special reason (e.g. sensitive analog signals with low signal level).
Most maxon controllers have a metal housing. Ideally the housing is mounted electrically connected on a metal plate. Hence, the different cable shields can easily be mounted with large connecting areas on the mounting plate giving an ideal shield connection on the controller side. If such a mounting configuration is not possible, then connect the shields according to the operating instruction with as low a resistance as possible to the „Earth“ contact or the screw on the housing.
Connecting cable shields on both ends can produce loops. For sensitive anlog signals the incoming 50/60Hz interference may ask for cable shields which are connected only on one end. But as a rule, cable shields should be connected on both ends. The reason for interferences with both ends connected can be a insufficient earthing concept or a bad cable routing with large loops.
HF blocking by means of a ferrite core on a cable improves the interference stability against external interference couplings. This can be helpful to recognise when interference suppression has to be done on a machine exhibiting insufficient interference resistance during operation.
As a rule only complete units comprising of all individual components (motor, sensor, amplifier, position control, power supply, EMC/EMI filter, cables, etc.) should be submitted to an EMC test for CE conform, interference free operation.
- The motor cables must be shielded when used with a pulsed (PWM) controller.
- The shield must be connected on both sides (at the motor side on the housing or on an electrically connected mechanical construction).
- For DC motors without CLL, a suppression with decoupling capacitors directly at the motor is recommended due to the arc production in the commutator.
An additional EMC motor filter (e.g. like shown above) which partly or completely consists of additional capacitors can have a negative impact on a proper current measurement in case of PWM power stages like in use by maxon (and all modern) motor controllers. The current measurement can be permanently or sporadically wrong due to the additional EMC filter and finally result in an unexpected control reaction. It is just recommended to add such filters in case of DC motors which are supplied directly by a power supply or battery without the usage of a motor controller with a PWM power stage.
- Use shielded cables.
- Shield connected on both sides.
- Use a separate cable (not in motor cable).
- The pairs "channel A, channel A\", "channel B, channel B\" und "index channel I, index channel I\" must be twisted in pairs.
- At strong external interference level a shield (connected on both ends) may be necessary.
- The resolver cables must be shielded.
- The pairs "cos+/cos-", "sin+/sin-" and "resolver primary/GND primary" must each be twisted and shielded in pairs.
- On the resolver side, the shielding may not come into contact with the plug housing (motor housing) to prevent earth loops.
Analog signals (set values)
- A shielded cable is recommended.
- As a rule, shield connected on both ends. If problems with 50/60Hz interference occur, connect shield on one end only.
Digital I/O signals
- As a rule no shielding is necessary.