Arena Service Manual
11.3.2 Stepper Motor Drive Control
The heparin pump circuitry on the Blood Pump Power Board
drives a stepper motor (see 11.2.4), which controls the rate of
injection from the syringe. The stepper motor rotates a pinion
mechanism. The pinion moves the rack and the plunger foot
moves the heparin syringe plunger the same distance.
To increase the accuracy of the heparin pump during start-up,
when the heparin pump is on, the syringe holder arm has just been
engaged, and an end-of-stroke is detected, the motor will run at a
higher rate for up to 1.7 seconds to engage the gears.
The operator enters a desired heparin rate in milliliters per hour
(mL/h) via the front panel touch screen. The Single Board
Computer (SBC) displays this rate on the screen, converts it to the
appropriate heparin pump motor step rate, and passes the
information to the Blood Pump Controller and I/O Controller. The
Blood Pump Controller outputs a motor step rate clock signal to
the Blood Pump Power Board where the Blood Pump Power Board
energizes the appropriate stepper motor coils.
11.3.3 Stepper Motor Driving Monitoring
The motor step rate clock signal from the Blood Pump Controller
is also input to the I/O Controller board. The I/O Controller
monitors this signal to determine if the heparin motor is operating
at the appropriate speed. If it determines that an overspeed
condition exists, it disables the heparin motor via an enable line
that goes through a hardware line on the Blood Pump Controller
Board to the Blood Pump Power Board. The alarm signal is set to
11% over the desired rate. The alarm signal is also sent to the
SBC to cancel the stepper motor rate signal and create an audio
and visual alarm.
11.3.4 Bolus Infusion Control
Via the Touch Screen, the operator infuses a 0.3 to 5.0 mL bolus of
heparin into the extracorporeal bloodline with a 20 or 30 mL
capacity syringe (0.3 to 4.0 mL bolus for a 10 mL capacity
syringe). The SBC sends to the Blood Pump Controller and I/O
Controller boards the number of motor steps to be taken at the
bolus rate. During bolus infusion the I/O Controller board will
cause an overspeed alarm to occur if an excessive number of high-
speed steps occur.
11-8 157-1278-918 Rev A
April 2004
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