Logistat A500

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The Logistat A500 is a programmable logic controller that was brought onto the market by AEG in 1980.

It was the successor to the A400 and used the same structure and many of the I / O cards. After a few years, a simplified version called the A350 came onto the market. With the acquisition of Modicon by AEG, the product name Logistat was replaced by Modicon. With the sale of this part of AEG in 1994, the controller is now a Schneider Electric product . It has been used in a wide variety of areas over the past 25 years. They can still be found today in waterworks, sewage treatment plants and many industrial companies. A total of around 20,000 installations have been carried out by the systems of the A350 / A400 / A500 group. Another device type with the designation A800 is a PLC developed within the field of power converter technology, which largely differs in hardware and software from the A500 and is not, as one might assume from the type designation, a further development of this.

System overview

The devices can work in hierarchical architectures and also take on process control tasks. They are modularly expandable. The devices are basically identified as follows:

  • A = automation device
  • K = communication technology
  • B = control or display device
  • P = programming device

A500 data

The first ALU was the ALU821 equipped with an Intel 8086 and optionally with an 8087. It could address 1 MB with its 16 bit processor. The basic software was modularly pluggable on additional cards and could use more than half of the possible memory. Since the basic software was stored on EPROM , the service life is limited. The first 64k of the basic software had to be firmly attached to the ALU. The rest was plugged into SF8512 as needed. Since address space was also required for signal memories and the addressing of communication cards, almost 300Kb were available as user memory in RAM or EPROM. The range of possible I / O is around 5000 digital and analog. In addition to this "original ALU", other types were later used that no longer rely on the PMB bus (PMB = parallel microprocessor bus; memory bus) to access the memory. This series began with the ALU011 and was later expanded to include faster types. The programming remained compatible. The basic software and the RAM area were integrated on the ALU module. In order to allow the ALU to be changed without losing memory, a lithium battery can be clamped to 2 pins of the programming interface.

How the A500 works

The way the A500 works was essentially determined by the interaction of:

  • Storage
  • Central unit
  • I / O modules

The data flow between these components was perceived by different bus systems.

A contact with the buses (PMB, PEAB) was established by engaging the I / O modules with the connector on the rear.

Storage

The memory had an address space of 1 Mbyte. It can be divided into 3 areas:

  • User memory (RAM or EPROM)
  • Signal memory (RAM)
  • Basic software (EPROM)

Central unit

The central unit was the control and arithmetic unit of the A500. It controls the individual instructions (AWP) of a program according to the rules specified by the basic software (firmware).

  • Reading of external data and signals into the signal memory
  • Processing of this data
  • Calculations
  • Saving the processing results in the signal memory
  • Output of the results.

I / O modules

All modules that have a direct effect on the process are I / O modules. This includes:

  • Input / output modules for processing binary signal states
  • Input / output modules for processing analog signals
  • intelligent function modules (partly I / O modules with built-in processors, e.g. positioners, controllers, counter modules, etc.)

A distinction must be made between the I / O modules:

  • Front connection technology: The connection for the process signals as well as for the supply of the sensors and actuators was made via screw / plug-in terminals on the front.
  • Rear connection technology: The connection for the process signals as well as for the supply of the sensors and actuators was made via 48-pin plugs that were located on the rear of the assembly.

PMB basic subrack

The PMB (parallel microprocessor bus, memory bus), which was located on the back wall of the central subrack. The central units (e.g. ALU821), the memory modules (SC 8256, SF 8512), the monitoring module (UKA 02x) and the coupling modules (BIK, KOS, KP ...) were connected to it. Each PMB participant occupies a certain part of the available address space (memory). Which addresses have been assigned to the respective participant is defined on the hardware of the individual modules via bridge settings (no slot addressing).

PEAB basic subrack

The PEAB (parallel I / O bus), which was located on the rear wall of the central subrack and the expansion subrack DTA 025. PEAB participants are UKA 024, ALU 150, ALU 011, ALU 061 as well as the I / O assemblies designed using rear connection technology. The I / O slots for the PEAB were located in the expansion subracks DTA 025 and in the central subracks DTA 024 and DTA 028. A fixed address was assigned to each PEAB slot. The addressing is therefore independent of the module with which the respective slot was equipped (slot addressing). The addresses for ALU and UKA were assigned automatically by the system.

programming

In the beginning, programming was carried out exclusively using Dolog 80B, a block language integrated in the controller. The programming was carried out by terminals directly on the control. When the first PCs became affordable, programming could also be done offline on the PC. The programs were written with a text editor (ALTER) and then translated with the A500 software and loaded into the controller. A further development of the A500 is Modicad E, with which you could carry out graphic programming in block technology. A Windows software (A500 Classik) has recently been developed. The 2nd programming software for the PC is Dolog AKF35. For the first time programming based on DIN 19239 in STL, LAD and FBD was possible.

communication

Communication with the A500 takes place with the IKOS coupling, an AEG in-house development and an integral part of the AEG automation devices (Micro / A120 / A250 / A350 / A500).

IKOS

The "Integrated Communication System" (IKOS) is defined as a local network with open communication (OSI) and bit-serial transmission. The integrated communication system is based on the serial system bus SEAB and the lower 5 layers of the ISO / OSI reference model.

According to IKOS, coupling is understood in the broadest sense as the connection of two or more communication participants (coupling participants) for the purpose of data exchange. The transmission path on which this data exchange takes place is called a bus. The data (messages) to be transmitted are coded and transmitted in the form of telegrams. The way of coding (telegram structure) and the type of transmission (serial / parallel) is called the communication procedure (AEG coupling procedure).

For the application level, protocol specifications based on IKOS system message paths and SEAB procedures were defined as AEG standards SKOS (A250) and BKOS (Micro / A120) for the operating and programming functions (PUTE). These protocols are laid down in the AEG IPA 90 development guidelines.

SEABKOP (A500 ↔ DPC400) or "B500" use the user data field (D3 to D128) available in a Modnet-1N telegram by means of a directed message path for data transport.

SEAB

The serial system bus (SEAB) is a transmission system on which all messages are transmitted bit-serial between the stations in the form of telegrams. It served as a generic term for the SEAB 1F, SEAB 1N and SEAB 2NP system buses implemented in the AEG. You serial plant buses implement layers 1 and 2 of the ISO-OSI layer model.

In the course of the development of automation, the term “SEAB” was replaced by “Modnet” by structuring the communication hierarchies. On the basis of the ISO / OSI layer model, AEG defined three different implementation variants for data exchange in all technology areas:

  • Modnet 1: field level - coupler: 1 / SFB, 1 / N, 1 / P, 1 / F, 1 / W etc.
  • Modnet 2: Process bus coupler: 2 / NP (Token BUS), 2 / ND.
  • Modnet 3: Backbone coupler: 3 / MMSE. (MAP 3.0)

The Modnet 1 implementation variant with the coupling modules for 1 / SFB (Bitbus), 1 / N, 1 / F and programming device coupling (V.24) use the SEAB telegram types or procedures (OSI layer 2) for data transmission.

SEAB 1F

AEG telecontrol bus under GEADAT, based on DIN 19241

  • Optimized for slow transmission channels and long distances
  • Transmission rate 300 to 19200 baud
  • Distance range unamplified up to 15 km, depending on the transmission rate
  • Number of participants 127 (address 0… 126, 127 = global address)
  • Baseband transmission technology with GDÜ
  • Frequency transmission with MODEM
  • Transmission medium telecommunication cable
  • Transmission type sending with acknowledgment, reading and broadcast
  • Single character transmission 2/4 bytes
  • Error protection HD = 4, lengthwise and crosswise parity
  • Error correction by repetition
SEAB 1N

AEG process bus under IKOS, based on DIN 19241

  • Optimized for message transmission in blocks of up to 128 bytes
  • Transmission rate 300 to 19200 baud
  • Distance range unamplified up to 10 km, depending on the transmission rate
  • Number of participants 128
  • Baseband transmission technology with GDÜ
  • Frequency transmission with MODEM
  • Transmission medium telecommunication cable
  • Transmission type sending with acknowledgment, reading and broadcast
  • Block transfer of up to 128 bytes, including 126 bytes of user data
  • Error protection HD = 4, lengthwise and crosswise parity
  • Error correction by repetition
SEAB 2NP

AEG process bus under IKOS, according to PROWAY C, IEEE 802.4

  • Optimized for message transmission in blocks
  • Transfer rate 5 Mbaud
  • Distance range unamplified up to 0.8 km
  • Number of participants 40
  • Carrier band transmission technology
  • Transmission medium coaxial cable

Sources: AEG manual "Terms of communication technology"

Others

Nevertheless, they have not caught on in the jungle of communication protocols. For this reason, there are now other protocols that are emulated by the A500 and / or its communication modules.

Front connection technology

The front connection technology developed later in connection with the A350 and A250 was also implemented on the A500.

Experts |

The expert modules POS001, POS011 and DOZ001 among others were an important development of the A500. These allowed quick reactions, regulation and control. This in conjunction with a PLC and thus fully integrated into the system programming. In addition, AEG Stromrichtertechnik forms an important interface for using the A500. Several digital and partially digital converter types of the first and second generation that were manufactured in Berlin have an interface to the A500 fieldbus SEAB-1-SFB.

use

The A500 was used in particular as a PLC in larger control centers. However, the centralization of inputs and outputs is no longer common today. The front connection technology was also unable to fully meet the new decentralized concepts. Therefore, and because of its very high price, this device is no longer up-to-date. In many applications, the A500 has been in operation for longer and for years without any noteworthy failures. This speaks for the high production quality that few PLCs have achieved to date. A500 was still found in sewage treatment plants, chemicals and production plants in Asia.

spare Parts

Spare parts for the A500 were still in great demand until 2000. Then, however, old controls in Europe and the Far East were completely replaced and the A500 is definitely history.

A130, A250, A350, A500 spare parts, migration strategies

For systems that are equipped with the A250, A130, A350 and / or A500 systems, OHP supplies new or spare parts, so that the operation of systems with these controls is ensured in the long term. In particular, with the migration to new ALUs of the @ 250 series, OHP offers a cost-effective and elegant alternative for upgrading to the latest technology and thus securing the systems for the future. With the new @ 250 systems, OHP has developed a strategy that migrates the A (automation) and U (telecontrol) devices into a new and long-term available automation and telecontrol series with minimized costs and time expenditure. For the A350- / 500, this migration strategy can be used directly on the front connection technology.

The main advantage of this strategy is that the existing I / O level is retained. This eliminates high costs for new I / O modules, assembly and wiring, which means that the system can be modernized with significantly lower and more manageable costs and time.

The implementation of a modernization during operation can be precisely calculated, as there is no point of no return. If the system to be modernized has to go back into operation at a certain point in time, the previous ALU and, if necessary, the basic subrack can simply be plugged in.

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