Microprocessor Control of a Coolant Distribution Unit

Microprocessor Control of a Coolant Distribution Unit

       Identified is the use of a microprocessor to control a
CDU (Coolant Distribution Unit) of a water-cooled mainframe computer.
 The design involves a single card which is responsible for all CDU
operations including:  system water temperature regulation, pump
control, CDU operators control panel, CDU sensor reporting and error
recovery, and stand-alone control as well as supporting PCE commands.

      Hardware Configuration - An Intel 8-bit microprocessor provides
the CPU platform for implementation of the algorithms described
within.  Additional required hardware functions, such as extended I/O
and system interfaces, are provided by an IBM custom CMOS logic chip.
 Vendor analog circuitry including a 12-bit A/D, analog mux, filter
networks are used to acquire 8 signals from the 3 sensor types.

      Several levels of error detection are implemented within this
design in order to meet system requirements of large processors.
Examples of this are protocol checks within the custom logic module,
watch dog timers for use by the microprocessor and sensor data
windowing for external inputs.

      The analog acquisition is considered "cost reduced" since it
relies on filter network time constraints to provide the sample and
hold function.  This is considered unique to this application.

      Software Algorithms - One of the design highlights is the water
temperature regulation scheme.  The controller for the system water
temperature regulation is proportional and differential (PD).  The
control theory representation behind the PD controller is as follows:
      U(kT)=Kpxe(t)+(Kdx(de(t)))
                           dt where e(t) = error signal = temperature
difference between desired and actual, T = sampling period, Kp =
proportional constant, Kd = differential constant, and U(kT) is the
control signal from the microcontroller.  See the figure.

      Translation of the theory into an implementation on a
microcontroller yields the following equations:
      PR = Kp x (Ta - Td)
      DF = Kd x (Tp - T1) where PR...