【正文】 eeping the hands on the source code and being able to solve problems on your own and faster than industry are the argument for home grown solutions or open source solutions. The experience of many years of operations shows that which solution is the primary one does not matter, there are always areas where at least part of the other implementations exist. As a result heterogeneous systems have to be maintained. The support for different protocols is essential. This paper describes our experience with industrial control systems, PLC controlled turn key systems, the CCS tool kit EPICS and the operability between all of them. INTRODUCTION Process controls in general started at DESY in the early 80th with the installation of the cryogenic control system for the accelerator HERA (HadronElektronRingAnlage). A new technology was necessary because the existing hardware was not capable to handle standard process controls signals like 4 to 20mA input and output signals and the software was not designed to run PID control loops at a stable repetition rate of seconds. In addition sequence programs were necessary to implement startup and shutdown procedures for the plex cryogenic processes like cold boxes and pete pressor streets. Soon it was necessary to add interfaces to field buses and to add puting power to cryogenic controls. Since the installed D/3 system[1] only provided an documented serial connection on a multibus board, the decision was made to implement a DMA connection to VME and to emulate the multibus board?s functionality. The necessary puting power for temperature conversions came from a Motorola MVME 167 CPU and the field bus adapter to the in house SEDAC field bus was running on an additional MVME 162. The operating system was VxWorks and the application was the EPICS toolkit. Since this implementation was successful it was also implemented for the utility controls which were looking for a generic solution to supervise their distributed PLC?s. A SELECTION OF PROCESS CONTROL SYSTEMS AT DESY DCS (D/3) As a result of a market survey the D/3 system from GSE was selected for the HERA cryogenic plant. The decision was fortunate because of the DCS character of the D/3. The possibility to expand the system on the display and on the I/O side helped to solve the increasing control demands for HERA. The limiting factor for the size of the system is not the total number of I/O but the traffic on the munication work. This traffic is determined by the total amount of archived data not by the data configured in the alarm system. The technical background of this limitation is the fact that archived data are polled from the display servers whereas the alarms are pushed to configured destinations like alarmfiles, (printer) queues or displays. SCADA Systems with DCS Features (Cube) The fact that the D/3 system mentioned above had some hard coded limitations with respect to the Y2K problem was forcing us to look for an upgrade or a replacement of the existing system. As a result of a call for tender the pany Orsi with their product Cube came into play [2]. The project included a plete replacement of the installed functionality. This included the D/3 as well as the integration of the DESY field bus SEDAC and the temperature conversion in VME. The project started promising. But soon technical and anizational problems were pushing the schedule to it?s limits which were determined by the HERA shutdown scheduled at that time. The final acceptance test at the vendors site showed dramatic performance problems. Two factors could be identified as the cause of these problems. The first one was related to the under estimated CPU load of the 6th grade polynomial temperature conversion running at 1 Hz. The second one was the additional CPU load caused by the plex functionality of the existing D/3 system. Here it was underestimated that each digital and analog input and output channel had it?s own alarm limits in the D/3 system. In a SCADA like system as Cube the base functionality of a channel is to read the value and make it available to the system. Any additional functionality must be added. Last not least the load on the work for polling all the alarm limits – typically for a SCADA system – was also driving the work to it?s limits. Finally the contract with Orsi was cancelled and an upgrade of the D/3 system was the only possible solution. It was finally carried out in march 2021. In any case it should be mentioned that the Cube approach had the advantage of a homogeneous configuration environment (for the Cube front end controllers) – pared with heterogeneous environments for ?pure? SCADA systems. SCADA (PVSSII) The H1 experiment at the HERA accelerator decided to use PVSSII for an upgrade of their slow control systems[3]. The existing systems were developed by several members of the H1 collaboration and were difficult to maintain. The decision to use PVSS as a replacement was driven by the results of an extensive survey carried out at CERN by the Joint Controls Project [4]. PVSS is a ?pure? Supervisory And Data Acquisition System (SCADA). It provides a set of drivers for several field buses and generic socket libraries to implement munication over TCP/IP. The core element is the so called event manager. It collects the data (mostly by polling) from the I/O devices and provides an event service to the attached management services like: control manager, database manager, user interface, API manager and the built in HTTP server. The PVSS scripting library allows to implement plex sequences as well as plex graphics. Compared with other SCADA systems PVSS es with one basic feature: it provides a true object oriented API to the device?s data. One major disadvantage of SCADA systems is the fact that two databases,