PDQ-II

The PDQ-11 was a specialized computer from 3-I (Information Instruments, Inc), later Allen-Bradley. The PDQ-II was a solid state programmable controller designed to be rugged and reliable enough to be installed in industrial applications. It was also a device which could be installed, and maintained by existing plant personal. As a solid state equivalent of relay control panels, the main advantage of the PDQ-II (and literally all programmable controllers) was that changes can be made via its program, instead of editing volumes of wiring schematics followed by the time consuming process of actually rewriting the relay control panels to match the updated drawings. And while the PDQ-II was a “first generation” PLC, the product’s block diagram clearly shows the very familiar representation of the components that would go on to become standard with most all programmable controllers.
The first unit was delivered in June 1969 to General Motors Hydra-matic division and used to control a gear grinding machine. Its design as a "programmable machine controller" was patented in 1973.
To re-program this PDQ-II, a Boolean program was written to punch a paper tape from a teletypewriter using a minicomputer interface. A special loader was used to load the program.
Each PDQ-II System consisted of eight types of components. As shown in the above image, these included the Logic Package (aka PLC Chassis or Rack) into which Logic Cards and a Memory Chassis would be installed.
The Logic Package itself included a power supply, cooling fans, ports to connect to multiple Input Output Packages and Programming Devices, two slots for Logic Cards, and a large slot for the Memory Chassis.
The two Logic Cards (aka Control Logic Modules) supported up to four internal timers, ranging from 0.1 ms to 70 hour time periods. And the Memory Chassis had slots for up to four 1K 8-Bit Random Access Core Memory Modules.
The Input/Output Package, also known as the I/O Chassis, is where the Input and Output Modules were installed, with each module having its own Plug-in Blocks (aka Removable Terminal Blocks.)
The chassis included a total of eight slots. The first four slots were narrower than the second four, and were used for the input modules. The second four wider slots could accept any combination of Output, Indicating Control Storage, or Analog Timer modules.
As far as I/O Module types are concerned, the PDQ-II system supported 120vac and 24vdc Inputs, as well as 120vac, 24vdc, and Relay Outputs. Each module type was capable up supporting up to 16 I/O Points, and each I/O Point had its own Indicator Lamp.
Output Modules were also individually fused and included Fuse Blown Indicator Lamps. The 120vac TRIAC and 24vdc Open Collector Output Modules supported up to 2 amps, and the N.O. Relay Output Module supported 35va (1 amp fused.)
The PDQ-II also supported up to a total of Four I/O Chassis, with a maximum of 250 Inputs and 250 Outputs.