Smiths Medical Medfusion 3000 Series, Technical & Service Manual

Page: 51 / 184

Theory of Operation
45 40-5648-51B
Sensors interface description
Motor speed detection
The digital sense signal is created by using a reflective
infrared optical sensor to sense a motor-coupled en -
coder as the motor rotates. The microprocessor mea-
sures the period of the signal created by the encoder.
Syringe sensing description
The syringe sensing system senses the syringe bar-
rel size, senses the plunger end cap is secured by the
mechanical flippers, and the syringe flange (ears) are
located in the pump’s syringe flange locating device.
•
The circuit for sensing the plunger flippers is part
of the plunger printed circuit function.
Syringe size sensing
Syringe sensing is accomplished by using a potenti-
ometer which changes its resistance with the barrel
diameter. The potentiometer is excited with a preci-
sion 4.096v voltage reference and the potentiometer’s
output is monitored through channel 2 of the system
A/D.
•
The sensing system requires calibration to deter-
mine offset and gain. Calibration values are stored
in non-volatile (serial EEPROM) memory.
Syringe flange (ear) sensing
Syringe flange (or ear) sensor is used to detect if the
syringe flange is installed in the flange-holder on the
side of the pump.
An infrared optical interrupter detects
when the
flange-locating device is in a valid position. A prop -
erly loaded flange causes the optical path to become
uninterrupted allowing a direct path from the infrared
emitter to the detector.
• The emitter is enabled by the signal syringe_ear_
snsr_enbl when set to logic low.
• The sensor output, syringe_ear_detect, pro-
duces a high logic state when the flange is properly
loaded.
• The state should be logic low anytime the syringe
ear (flange) is not installed or syringe_ear_snsr_
enbl is inactive.