Issue
What is the unit load (UL) of the SpaceLogic SP90 PIBCV Actuators that will help me to calculate how many SP90 PIBCV Actuators can be added on ComA and ComB of a SmartX Server.
Product Line
EcoStruxure Building Operation, Field Devices
Environment
- SpaceLogic SP90 PIBCV Actuator
- SmartX Server
Cause
Require the Unit Load (UL) of the SpaceLogic SP90 PIBCV Actuator to calculate the number of actuators allowed on the RS-485 network.
Resolution
The Generic application note AN01 can be applied with answers to the transceiver interface attributes below. The SpaceLogic SP90 PIBCV Actuator range uses the SN65HVD1780DR transceivers which are a failsafe transceiver (not requiring bias) and reduced 1/10 UL. In addition, there are no local bias resistors and therefore the 1/10 UL of the transceiver would be the total UL presented to the bus by the SpaceLogic SLP Room Unit.
| Transceiver | Xcvr Unit Load | Xcvr Failsafe | Adaptor Circuit Bias | Circuit Bias Load | Total Unit Load | Isolated 485 Bus |
|---|---|---|---|---|---|---|
| SN65HVD1780DR | 0.1 | Yes | None | None | 0.1 | No |
Based on the above the total number of devices can be calculated as 32/0.1 = 320.
The BACnet MSTP standard specifies that the address range for BACnet master devices is 0-127 and therefore a SmartX Server is limited to 127 devices per com port (254 total per Server) so this should effectively be the limiting factor. However, the documentation recommends using only up to 64 devices with the same RS-485 transceiver, or 32 devices with different RS-485 transceivers.
Since the SpaceLogic SP90 PIBCV Actuator does not have an isolated RS-485 interface it conforms to Generic RS-485 Network Device Configuration 1 in EBO Webhelp. A network consisting of only SpaceLogic SP90 PIBCV Actuators should only require a 120-ohm termination resistor at each end of the bus and not require any bias resistors.
Also, check out the SmartStruxure-RS485-Controller Unit Load Quick-Help video on the Exchange.
