Cloud Electronics CDR-1B - Manual (Page 8)

CDR‑1 & CDR‑1F Installation Guide v2.0 8
Cable length and DC power considerations
The DCM-1/e’s internal PSU has sufficient capacity to power 8 CDRs (i.e., one per
zone) provided cable runs are not excessive and good quality cable and connectors
are used. If a system has more than 8 CDRs in total, one or more additional PSUs will
certainly be required. The probability of correct operation is a function of cable length,
cable and connector quality, the number of CDRs daisy-chained, and how many of them
are at a great distance from the DCM-1/e.
The maximum recommended cable length of the CDR network for reliable data
transmission is 1 km. This figure applies either to the total cable run between the
“farthest” CDR and the DCM-1/e if a single daisy-chain of CDRs has been employed
(as in (b) on page 6), or to the total run between the most remote CDRs if the
DCM-1/e is in the “middle” of the chain (as in illustration (a) on page 6). Cable runs
longer than this may work satisfactorily, but this cannot be guaranteed. Note that the
1 km figure is a maximum over which data may be reliably transmitted, not over which
a set of CDRs may be reliably powered. In all systems, it is the power distribution which
will limit maximum cable length, not the data.
If a CDR is found to operate unreliably, it should be powered independently from a
local PSU. The Cloud CPM-PSU is suitable for this purpose, and should be connected
to the EXT POWER socket at the rear of the CDR. In the case of the CDR-1, this is
a coaxial socket, mounted vertically on the PCB to the right (viewed from the rear).
See diag. on page 11. In the case of the CDR-1F, the EXT POWER socket is a 2-pin
5 mm-pitch screw terminal type connector below the RJ45 connectors; a mating male
connector is supplied with the unit. See diag. on page 13.
Note: Wiring convention of the external PSU is unimportant, as the CDR incorporates
a bridge rectifier circuit which allows it to accommodate either polarity of connection.
Note that any further CDRs connected to the POWER OUT connector will be
powered by the external PSU.
If a third-party external PSU is to be used, it should be rated at either 12 – 24 V DC or
9 – 17 V AC. The current consumption of a CDR is 50 mA at 12 V.