Capacity limits for controllers

Description of controller capacity	Limits
Fastest module scan time	100 ms PK controllers - 25 ms
Simultaneous debug sessions	4
I/O cards per controller	64
DSTs per controller	SD Plus/SQ/MD Plus/MQ controllers - 750 SD Plus/SQ/MD Plus/MQ controllers interfaced to PROVOX I/O - 750 MD Plus/MQ controllers interfaced to RS3 I/O - 750
	SX/MX controllers - 1,500 SZ controllers⁽¹⁾ - 1,536 SX/MX controller interfaced to PROVOX I/O - 1,500 MX controller interfaced to RS3 I/O - 1,500
	PK controller has 4 sizes: PK100 - 100 DSTs PK300 - 300 DSTs PK750 - 750 DSTs PK1500 - 1500 DSTs
Unsolicited data reporting⁽²⁾	SD Plus/SQ/MD Plus/MQ controllers - 2,000 exception reports per second
Unsolicited data reporting⁽²⁾	SX/SZ/MX/PK controllers - 4,000 exception reports per second
Maximum incoming unsolicited exception reports
	SD Plus/SQ/MD Plus/MQ controllers - 250 per second
	SX/SZ/MX/PK controllers - 500 per second
Maximum exception reports from one node to another node	750 per second
Write operations per node	SD Plus/SQ/MD Plus/MQ controllers - 20 per second
Write operations per node	SX/SZ/MX/PK controllers - 40 per second
Controller Object Identifiers⁽³⁾	MD Plus/SD Plus controllers - 10,000
Controller Object Identifiers⁽³⁾	MQ/MX/SQ/SX/SZ/PK controllers - 16,000
Virtual Control Object Identifiers⁽³⁾	16,000
Function Blocks per module	250⁽⁴⁾
SCADA tags	3,200
Nesting levels per control module	6
Controller performance minimums	SD Plus/MD Plus FreTim - 20% ⁽⁵⁾
	SD Plus/MD Plus with assigned CIOC FreTim - 28%⁽⁶⁾
	MQ/MX/SQ/SX/SZ/PK - Perf_Index > 1
Controller free memory minimum⁽⁷⁾	SD Plus/MD Plus - 4.8 MB MQ/MX/SQ/SX/SZ/PK - FREMEM_INDEX > 1
Maximum reporting rate	Controller and remote I/O cards - 100 ms
Maximum reporting rate	Controller and CHARM I/O Cards (CIOC) - 50 ms

⁽¹⁾ Up to 4 WIOCs, CIOCs, Zone 1 Remote I/O nodes and Zone 2 Remote I/O nodes can be assigned to an SZ controller.

⁽²⁾ Develop configurations using a recommended limit of 1,000 parameters per second. Exceeding these recommended limits may affect system performance.

⁽³⁾ The controller uses object identifiers to keep track of remote items such as modules with which it is communicating. Each connection with a remote item consumes one object identifier. Maintain the FreOID parameter value above 2,000. A FreOID parameter value below 2,000 may result in interrupted control and communication failure. If the FreOID value is low, you can increase it by decreasing the number of one or more of the following: the devices communicating with the controller, the modules from which the controller reads data, the modules running in the controller, and various I/O items (for example, associated I/O cards, channels, datasets, ports, and so on).

⁽⁴⁾ The practical number of function blocks per module depends on a number of factors including configuration and associated I/O.

⁽⁵⁾ Maintaining the free time above the recommended level ensures overhead to handle plant upsets, alarm bursts, and so on. Controller redundancy affects controller loading, as described below.

⁽⁶⁾ Controller communications with CIOCs is part of the COMMS task that typically happens outside the Control CPU in what is known as the System CPU. The higher FreTim low limit for controllers communicating with CIOCs ensures that there is at least 20% actual CPU idle time on the controller to handle burst conditions.

⁽⁷⁾ Maintaining the recommended amount of free memory ensures that modules can be applied to the controller through a partial download, in most cases. Batch systems dynamically use this free memory when loading/unloading phases. It is recommended that you maintain 10% of the available user memory free to allow the memory management algorithm to optimize the free memory.

Note

For M-series and SD Plus controllers, redundancy has an impact not only on controller FreTim but also on controller idle time (shown by the Time Utilization Chart in DeltaV Diagnostics). Redundancy typically requires at least 10% more controller CPU than the same configuration in a simplex controller. Larger configurations (more modules, more parameters) require more CPU time for redundancy processing.

Note

SZ controllers (SIS controllers) do not support local I/O.

Related information

Controller redundancy

SIS Controller Modbus port