From the perspective of automation technology the function of the equipotential bonding is not put into question because the functionality is presumed and the points of contact are mostly seen in the low voltage system. However, in the meantime it was exposed that a secure and solid working communication network, including the bus system, is related with the function of the equipotential bonding. Straying currents and currents of higher frequency which are often caused by frequency converters, mostly use the shield of our data cable as return current flow instead of the intended equipotential bonding system.
Just relying on gut feeling, or making intuitive statements about the quality of existing shielding and earthing measures is rarely a good idea. The only way to ensure good equipotential bonding is proof by measurement. The mesh resistance measuring clamp EMCheck® MWMZ II is the right tool for this purpose. In this way, you meet the requirements of DIN EN 50310, which is cited in the new guideline “Functional potential equalization and shielding of PROFIBUS and PROFINET” from the World Association PROFIBUS & PROFINET International (PI).
Highlights MWMZ II Mesh resistance measuring clamp
- Measuring of earth loop resistance and earth loop inductivity
- First-time: Display of contact voltage
- Alert when detecting a dangerous voltage
- Recording of up to 300 measurements incl. time stamp
- Easy handling to keep the clamp open
- Good visibility of all displayed data via OLED display
Equipotential bonding measurement – reference values & mode of functioning
EMCheck® MWMZ II consists of two coils. The first coil induces a voltage of a defined level and with a defined frequency of 2083 Hz. The second coil measures the current induced by coil one in the set frequency range. The ratio of these two values is used to determine and display the alternating current resistance (impedance). The measurement is made without any interruption and can also be carried on conductors which already carry currents during their normal operation.
- The shield loop resistance of data cables (for example: bus cables) should have a maximum impedance value of 0.6 ohms.
- PE/PA loop resistances should be in the range of an approximated impedance value of 0.3 ohms.