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Driver User manual Document

**Note on the versions:
The previous versions – PSDIRECT 2.7.6 & Backend 7.10.57.004 are a compatible pair only to each other Versions PSDIRECT 2.7.8 & Backend 7.10.58.002 are compatible with older versions(not recommended) before above and future versions will not have compatibility issues

Siemens S7 PLC Emmulator for testing & training

Purchasing the Driver

The PSDIRECT driver is licensed via the CiTect key please order option CT305140 from your nearest Citect Dealer

Introduction

In large applications where CitectSCADA has to talk to many Siemens PLC's, a need has arisen to have a higher performance Siemens Driver interface. Simatic Net has a lot of limitations on the number of PLCs it can connect to and also the performance of the Siemens API has been an issue. Citect also needed a way to optimise the way the SCADA communicates to the PLCs, because it was too easy to build setups that overwhelmed the S7NT driver - particularly if the user attempted to poll large configurations of Function block instance DB's directly (User Defined types).

The ProSCADA Citect direct interface driver is a front-end / back-end driver, meaning that the driver consists of two parts:

• The back-end server polls the data from the PLC's at configurable intervals.

• The back-end puts the data in a memory cache.

The front-end is a native Citect driver which reads the data from the cache instantly with 0 delay (does not poll the PLC's).

Advantages over the traditional Citect Drivers

This has the following advantages:

1. The Polling of the data is completely de-coupled from the rate at which the clients are requesting it, which means the clients cannot choke up the IO server with requests - no matter how badly the system is configured.

2. With a traditional Citect Driver, all polling is Dynamic & client driven. With this driver each block of data has an individual poll time. This allows each block of data to be optimised to poll as SLOW as is acceptable for that sub-application. This then leaves more resources available for other data that needs to be faster. For example: poll analogs at 5 second interval, setpoints & run-hours at 30 second intervals. Operator perception of speed is associated to digital status and alarm inputs. These can be polled at 0.5 seconds intervals.

3. The data is already available when a client polls it and data is displayed immediately without delay. For example popup screens open instantly with data from the cache.

4. The back-end polls raw blocks of data from the PLC. The front-end can then request any data type from this one polled block. This results in substantial efficiencies when you have many mixed data types in close address proximity. For example: Siemens Instance DB's (User Defined types) like the PID loop DB's are very complicated structures containing floats, words & bits. The Citect S7NT driver would generate a poll for each data type whereas this driver would read the information in one network poll block of bytes to be stored in the cache, the Front end driver then processes a Citect Driver request For each datatype from the same cached data.

5. Communications can be configured and debugged outside Citect. Data can be read from the same cache using a simple OPC client before or while Citect is running.

Advantages over the Siemens Softnet Solutions

This section refers to the Siemens Ethernet back-end. To setup Siemens Simatic Net on a PC and to test the communication can be very tedious. Multiple IO servers have to be used to communicate to more than 20 PLC effectively.

The ProSCADA driver will take 5 minutes to install and run a test with OPC (An Example Citect project is supplied OPC is not used with CiTect). The driver works with any standard 10MB, 100MB or 1GB Ethernet card. To date more than 50 PLCs on a single system have been tested with one standard 100Mb card. More Ethernet cards can be used to communications to PLCs, however there are no real performance or reliability gains. The driver works equally well sharing Citect, Windows workgroups, & Siemens ISO thru 1 Ethernet card. A good Ethernet switch handles different link speeds & network node isolation.

Performance: Siemens has marketing propaganda scaring people into buying their expensive cards with graphs showing performance bottlenecks at the PC card. Our experience is different. The PLC's are the bottleneck & the total Ethernet bandwidth used by the Scada PC Ethernet card is < 5% typically. This driver maximises the communication to all the PLC's on your network by implementing a multithreaded parallel polling strategy. This driver supports up to 64 PLC's on one Network. It has been proven on a system with 50 PLC's & 80 000 IO.

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