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Limitorque QX Electronic Actuator FCD LMENIM3306-06 – 07/14
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Table 3.5– Loop topology connections
Terminal Block Number DDC
4 DATA-A1* (-)
5 DATA-A1 (+)
14 DATA-A2* (-)
13 DATA-A2 (+)
3 Surge Protection
In terms of voltage, DATA is negative with respect to DATA*.
NOTE: Surge protection must be grounded to be effective.
NOTE: Ground each segment of the cabling at only one point to prevent ground loops, which can affect system
performance. Verify the actuator is properly grounded.
Limitorque defines an effective local earth ground as the M3 taps on the housing next to the terminal block. See figure
3.14.
NOTE: Safety ground may not be disturbed.
NOTE: Shielding is not sufficient to prevent induction of stray voltages onto signal leads from the power lines.
A network wiring diagram for a loop is shown in Figure 3.13.
After installation is complete and prior to operation, inspect the network cable and its connection to each field unit for
the following:
There should not be:
• Nicks in the insulation—this can cause a short to the grounded shield.
• Cut strands in a stranded conductor—this can cause a poor connection and eventually an open circuit.
• Cable armor shorted to the cable shield/drain wire—this may not be at ground potential and could be subject to
lightning surges.
• Shield/drain wire grounded at more than one end of each cable segment (the section between each adjacent actuator
on the loop). This will avoid ground loop problems.
• Ground/earth connection except at true ground potential and effective at all times.
3.3.8 Foundation Fieldbus Installation
Ensure that the Foundation Fieldbus cable type is Belden 3076F, or another cable that is within 5% of the following
specifications.
• Characteristic impedance: 100 ohms @ 31.25 kHz
• Resistance, each wire: 7.32 ohms/1000 ft
• Attenuation: 0.914 dB/1000 ft @ 39 kHz
• Capacitative Unbalance: 3.6 pF/ft
Using other cables may result in decrease of internodal distance and/or an increase in communication error.
Particular care should be taken when terminating twisted-pair shielded cables in a FF control network. Avoid nicks, cuts,
or abrasions in the insulation of data communication cables, since this may result in inadvertent ground connection.
Also, excess cable should be cut, not coiled or looped, to prevent noise induction into the network.
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