When conveying solids and liquids through hoses, the friction of the conveyed material on the wall creates frictional electricity.
To determine the electrical properties of a hose - and its tendency to electrostatic charging - NORRES tests the conductivity of hoses in accordance with the requirements of DIN EN ISO 8031. Therefore the hose is placed on a non-conductive surface.
At NORRES, every produced batch of hoses is tested for it's conductivity and electrical properties. These values are archieved in a traceable way and the customer has the possibility to get a suitable test certificate to every purchased batch.
Measurement of surface resistance
The surface resistance of the hose is determined with conductive sponges. The sponges are connected to the measuring device with crocodile clamps and attached to both sides of the hose. To reduce contact resistance, the sponges need to touch the entire surface of the hose.
Measurement of contact resistance
When measuring the contact resistance, one conductive sponge is removed and the crocodile clamp is attached to the wire - or cord - of the hose instead. The resistance between the inner wall of the hose and the conductor is measured.
Measurement for the TRGS
Which hose according to TRGS 727 can be used for a potentially explosive area was determined for each hose type by NORRES in cooperation with external experts. The measuring method is described in DIN EN ISO 8031 and is based on the above mentioned measurement of the contact resistance. The difference is, that in this case sponge and wire are on the same side. The measured resistance is then converted into the specific resistance required by TRGS 727.
Other measurement types
Depending which product is tested, the measurements can be adapted to the respective product properties. For example, highly conductive joints or hoses from the NORRES product range do not use a sponge impregnated with conductive agent, but a silver conductive lacquer in a special composition and/or a metallic test core to minimize the contact resistance between electrode and clamp.
- Resistance > 1. 0x10 e6 is measured with 500V test voltage (Metriso Tech).
- Resistance < 1. 0x10 e6 is measured with 40V test voltage (Voltkraft multimeter).