Connecting transducers

Shielding design

Sources of interference can cause electromagnetic fields which can induce interference voltages inductively or capacitively via the connection cable and device housing in the measurement circuit and therefore interfere with the device function. It must be ensured that the devices used in the system also do not transmit any electromagnetic interferences. Electromagnetic compatibility (EMC), which encompasses both the required electromagnetic interference immunity (EMI) and the permissible electromagnetic interference emissions (EME), has become increasingly important over the years.

According to the HBM Greenline shielding concept, the measuring chain is completely enclosed by a Faraday cage by appropriate routing of the cable shield. The cable shield is extensively connected with the transducer housing and is routed via the conductive plug to the amplifier housing. The influence of electromagnetic interferences is significantly reduced by these measures.

NOTE
All parts of the measurement chain (including all cable connection points such as plugs and couplings) must be surrounded by a closed EMC‐proof shield. Shield junctions must represent a full contact, closed and low‐impedance connection. This is the case for original HBM plug connections.

Ground connection and grounding

As the signal ground and shielding are separated in EMC‐compliant cabling, the shielding can be connected at more than one point to the ground, i.e. via the transducer (metal housing) and the amplifier (housing is connected to the earth conductor).

If there are differences in potential in the measuring system, a potential compensating line must be laid (reference value: Highly flexible stranded wire, wire cross section 10 mm2). Signal and data leads must be set up physically separated from current‐carrying power lines. Ideally, cable ducts made of sheet metal with an internal partition should be used. Signal ground, earth and shielding must be laid out as separated as possible.

In order to minimize the influence of electromagnetic interferences and differences in potential, the signal ground and earth (or shielding) are designed to be physically separate in the HBM devices. The mains earth connector or a separate earth potential lead should serve as the earth connection as is the case for example regarding potential compensation in buildings. The earth cable should not be connected to a radiator body, water pipe or similar objects.

Active transducer connection

Some modules can supply active transducers with a supply voltage of 5-24 volts.

When using the adjustable transducer excitation, electrical isolation from the supply voltage of the amplifier is not required.

The maximum permissible power consumption is 700 mW per channel and 2 W total. If the power consumption is more than 700 mW on one channel, the transducer excitation of this channel switches off. If the power consumption exceeds a total of 2 W, the device may switch off.

CAUTION
Check the correct voltage setting when connecting a sensor. Too high a voltage can destroy the sensor. The voltage value is a part of the MX module parameterization and can only be changed with a new parameterization. The sensor supply is switched off in the delivery condition.