Installation
1.9
Check the position of the terminators in the following topologies.
Figure 1.11 - Position of Terminators in Tree or Star Topologies and on the Bus
Power Supply
The power supply usually has an
output of 24 Vdc with capacity of a few ampéres. The power supply
can operate in redundant mode and it should failure indication and protection against surges,
transients and short circuits. Smar makes the DF52 power supply that meets these characteristics.
In terms of power supply signal, consider as acceptable values in practice:
•
12 to 32 Vdc in the PSI output (Active Impedance)
•
Ripple
(mV):
< 25: excelent;
25 < r< 50: ok;
50 < r < 100: acceptable;
> 100: unacceptable.
In terms of communication signal, consider as acceptable values in practice:
•
750 to 1000 mVpp: ok;
> 1000 mVpp: Very high. A terminator may be lacking.
Some barriers and segment protectors, like spur guards, have high impedance in series and can
produce signals up to 2000 mV and even allow the appropriate operation.
•
< 250 mVpp: Very low. It is necessary to verify if there is more than 2 active terminators, power
supply, etc.
Some devices have polarity, others not, so it is very important to assure the correct polarity of the
devices. All the devices are connected in parallel, that is, all the negative terminals together and all
the positive terminals together. The use of colored wires codified is recommended to distinguish the
positive from the negative.
Active Impedance
The active impedance avoids that the power supply low impedance lessens the communication
signal of the bus, allowing the feeding to be supplied in the same wire pair.
