Hill-Rom Isolette C2000 - Impeller Movement Detector (IMD) P.C. Board

Theory of Operation
Chapter 3: Theory of Operation
The controller provides DC power to the fan, sensor module, scale, SPO,
module (if available), airflow sensors, and door switches. These outputs are
current limited in the controller to protect the controller and the powered
device in the event of a short circuit or electrical overload. These outputs are
regulated to ensure the output voltage is within the voltage specification for the
powered device. The microprocessor feeds and monitors the outputs 1 and 2
into the A/D converter.
Impeller Movement Detector (IMD) P.C. Board
The IMD P.C. board is positioned so magnets pressed into the bottom of the
impeller pass directly over a hall effect sensor mounted to the P.C. board. The
IMD circuit monitors the hall-effect sensor pulse train produced by the
magnets when the impeller rotates. The speed of the impeller is measured and
compared with pre-determined maximum and minimum acceptance limits. If
the impeller’s rotational speed is too fast or too slow, an impeller error signal is
generated. The IMD circuit also detects if one, two, or all three magnets are
missing or an old impeller without magnets is being used. These errors produce
the same error signal to the controller as for low or high impeller speeds.
The system controller’s +12V through a 301Q resistor supplies the power for
the IMD circuit. This resistor and the load of the IMD circuit forms a voltage
divider that sets the LONG signal voltage which remains constant. U1, a
voltage regulator, supplies +5V DC to U3, the hall-effect sensor and U2, the
microcontroller. As the magnets pass above, the hall-effect sensor open-drain
output, U3-2, goes low detecting the magnets field. When this field is
removed, oscillator as a reference. When an error condition is detected U2-2,
the microcontroller’s output is driven low turning off Q1, releasing a portion of
the
load on the short signal allowing it to rise above the LONG signal voltage.
R2, the switch portion of the SHORT signal load, and R4, the unswitch
position of the SHORT signal load, are adjusted to provide approximately a 1V
swing between error and non-error outputs. Capacitors C1 and-C2 are provided
for system supply filtering.
The IMD P.C. board supports in-circuit programming (ICP) of the
microcontroller. Programming is done after the unprogrammed
microcontroller is populated with all the other components by connecting a
programmer to the pads labeled VPP, +5V, CLK, DTA, and GND.
lsolette® Infant Incubator Service Manual (man223rf) Page 3-17