SiemensPXC52Compact Freely Programmable Building Automation Station, 52 Physical Data Points, BACnet over LonTalk

Product Description

What this part is

A Siemens Desigo PX compact automation station, model PXC52. It is a freely programmable controller for HVAC and building services plant, carrying a fixed mix of 52 physical data points on the station itself so that sensors, valve and damper actuators, contactors and status contacts wire directly into it without separate I/O modules. Alongside the control logic it runs the management functions of a building controller: alarm handling, time schedulers, trend logging, remote access and access protection. Communication is BACnet carried over LonTalk.

Reading the designation

PX is the Desigo automation station family and C marks the compact model, in which the data point count is fixed in the hardware, as against the modular PX stations where I/O modules are added to reach the required count. The number 52 is that fixed physical data point total. The sibling PXC36 is the same concept at 36 points, and an -S or similar suffix on models in this family denotes a version with an integrated operator unit.

The point mix and what it accepts

Analogue inputs work on a 0 to 10 V signal. Binary inputs and outputs operate at 0 to 24 V DC with a maximum of 22 mA. Relay digital outputs are rated for up to 250 V AC at 2 A, which is what allows a fan contactor or a mains-voltage actuator to be switched from the station without an interposing relay. From Desigo V5 the station’s inputs and outputs are universal, so what were formerly fixed universal inputs and analogue outputs became parameterisable in the engineering tool — a point can be reassigned in software instead of by rewiring, which is the difference between a change taking minutes and taking a site visit with a screwdriver.

What the fixed point count means in practice

A compact station is the right economics when the plant is known and stable: one part number, one wiring schedule, no module inventory. The constraint is that it cannot grow. A modular PX station is the choice where point count is likely to expand, and a compact station reaching its limit is replaced rather than extended. The 52-point mix suits a mid-sized air handling unit, a boiler or chiller plant room, or a floor’s worth of terminal equipment.

Quantity and configuration

1 Pc. Automation station only. No operator unit, no engineering or plant program, no LonTalk network cable or terminators, no 24 V transformer, no DIN rail or mounting hardware, no field wiring terminals beyond those fitted and no licence.

Installation and setup notes

The station is a panel or DIN rail device inside a control cabinet, fed from a 24 V supply, with field devices landing directly on its own terminals. The plant program is engineered off-line and downloaded into the station, so a replacement unit carries no application until that download is performed; the program, not the hardware, is what makes the station specific to a plant. The BACnet device instance and the LonTalk addressing are set during commissioning.

Interchange guidance

Another PXC52 is the direct interchange, subject to the plant program being downloaded. The PXC36 and PXC36-S are related stations with a smaller point count and, on the -S, an integrated operator unit, so they are not substitutions where 52 points are wired. Modular PX stations use the same engineering environment but a different mechanical and I/O arrangement. Later Desigo PXC4 and PXC5 generations are a different hardware platform on native BACnet/IP and do not accept a LonTalk-era station’s program unchanged.