Notes Regarding Connectors And Wiring - Beckhoff EPP3504-0023 Short Manual

7.2

Notes regarding connectors and wiring

It is in the very nature of EtherCAT I/O modules/terminals/box modules that they have two connection sides:
one to the fieldbus for communication with the module, which is obligatory, the other to the signal/sensor/
actuator to facilitate proper use of the module. The "outer" connection side usually features contacting
options for connecting outgoing wires.
Only few I/O devices do not have a second side. Examples include the EL6070 license key terminal and the
EL6090 display terminal.
Notes and suggestions for dealing with the connection options are provided below
• Manufacturer specifications/notes for connection options must be followed. Any special tools that
may have been provided must be used as intended, so that gas-tightness is ensured through the
crimping pressure.
• Any detachable connection system is subject to a specified maximum number of connection cycles.
Each connection/disconnection operation results in wear through friction, mechanical stretching/
relaxation, possibly ingress of contaminants/gases/liquids/condensation, contact discharge,
modification of the electrical properties and of the contact point (ohmic contact resistance). In other
words, releasing/connecting a contact results in mechanical, chemical and therefore ultimately
electrical changes.
In terms of the application scenario it is therefore important to select suitable connection systems or
devices with suitable connection systems:
◦ For connections that are more or less permanent, it may make sense to use connectors/contacts
with a maximum number of mating cycles (as specified by the manufacturer) of 10 to 100 cycles.
This may be the case if devices are installed/wired only once, and over the entire lifetime rewiring
is only expected to become necessary during maintenance work.
◦ For connections that have to be detached on a regular basis, connectors/contacts with a maximum
number of mating cycles of 1,000 or higher should be selected. Such connections can typically be
found in laboratory environments, where the cabling may be changed several times each day but
high-quality contact must nevertheless be ensured over many years.
• When handling and assembling connectors/contacts it is essential to avoid contact with hand
perspiration/liquids, even for low-tech connections (open stranded wire, cage clamp/push-in). Acidic/
alkaline liquids may have a very aggressive effect on the contact surface and quickly lead to structural
changes and oxidation layers. These are very disruptive for analog measurements, particularly since
they undermine the reproducibility of measurements and can therefore result (if known) in large
systematic measurement uncertainty. It may be possible to rectify the problem by thorough follow-up
cleaning.
• The actual/expected load during operation must be taken into account when selecting connectors.
• Abnormal vibrations can lead to microfriction/corrosion and change the electrical properties, potentially
resulting in complete loss of contact.
• Temperature variations affect the mechanical strength of the connection and the spring forces in
metallic components.
• Exposure to gas or liquid can damage the connection, particularly if the gas or liquid penetrates to the
actual contact region and is unable to escape from there.
• Of high relevance for analog measurements is the electrical quality of the connection, both in the
short term during commissioning and over the service life under external influences and perhaps
repeated mating cycles. This is expressed in the repeatability of the transition. The influence should be
checked against the expected accuracy. Of particular relevance is the (frequency dependent) contact
resistance. Effects can be:
◦ Increasing the contact resistance results in a voltage drop when power is transmitted, potentially
leading to critical self-heating.
◦ The internal voltage drop can distort corresponding measurements. In order to avoid negative
effects, 4/5/6-wire connections should be used in SG/resistance measurements, since non-live
contacts are no longer affected by a distorting voltage drop. The popular 3-wire connection for
resistance measurement (PT100, PT1000 etc.) does not provide absolute protection, since the
singular line cannot be diagnosed. Current/voltage measurements in industrial environments are
less sensitive to contact changes.
EPP3504-0023 Version: 1.2
Mounting and wiring
207