Sigma 6000+ - Theory of Operation

THEORY OF OPERATION
The SIGMA International 6000+ is a volumetric infusion pump with optional Anti-Free Flow Clip and
Upstream Occlusion Sensor devices. Volumetric implies flow rate calibration in units of known volume,
ml/hr, rather than non-volumetric units of drops/min. The Anti-Free Flow Clip gives added protection
against accidental free flow. The Upstream Occlusion Sensor detects occlusions (closed roller clamps)
that may occur above the pump.
Pumps are generally unaffected by backpressure. They create just enough pressure to overcome the
backpressure they are confronted with. This is usually less than 1 psi when infused into a vein. IF the
backpressure increases, the pump’s pressure increases enough to maintain the selected rate. If pressure
increases to the occlusion alarm trigger point, the pump alarms and stops.
The SIGMA International 6000+ uses ultrasonic sensors for the detection of air in line and downstream
occlusion pressures.
MECHANICAL DESCRIPTION
The SIGMA 6000+ incorporates a peristaltic (tube squeezing) “finger” pump mechanism. Peristaltic
should not be taken to mean non-volumetric since there are both non-volumetric (drops/min) and
volumetric (ml/hr) tubing pumps.
The pump consists of a body, fingers, pressure plate and camshaft. The camshaft is driven by a stepper
motor controlled by the electronic circuits. The fingers ride on the cams and are driven to produce a
peristaltic motion in the pump. The tubing is squeezed between the fingers and a spring loaded pressure
plate. The spring loaded pressure plate allows the pump mechanism to self adjust to the tubing size
variations and variations during long term use.
The SIGMA pump incorporates an (optional!) Anti-Free Flow Clip mechanism. This clip is designed to
clamp the tubing closed when the set is removed from the pump to guard against accidental free flow.
SIGMA pumps are flow rate calibrated on known inner diameter (ID) tubing. The calibration principle is
always the same. Flow rate is a function of both pump speed, tubing inner diameter and tubing elasticity
(durometer). The electronic speed of the pump will remain with + .1% of the selected flow rate.
However, tubing variations make the overall flow rate variation somewhat greater (see specifications).
ELECTRONIC DESCRIPTION
Power Supply
-105-135VAC is fed through the power cord through a 1AMP fuse to a transformer. The transformer has
an output of approximately 21VAC that is fed into a bridge rectifier along with a-3300uf capacitor
mounted on the chassis behind the transformer. This produces 26-27VDC which is then fed to a LM317
. variable voltage regulator mounted on the chassis back panel and to a battery charge circuit on the
“MAIN” PCB consisting of U18 and Q8. The battery is attached to the main PCB through the 4A fuse
FI.
The regulated voltage is supplied to the Chopper Drive PCB via a 4pin molex connector. R23 adjusts the
regulated 13.9 VDC V+. R22 along with U18 and Q8 and their associated circuits set the battery charge
voltage at 13.6VDC. Regulated V+ is supplied to the main power switch Q7, D11 and on/off latch U8.
U8 is turned on or off with the ON/OFF key on the door panel which supplies a negative pulse to pin 10
of U8 when depressed. At the same time, a signal is fed back to the microprocessor via D10, U26 AND
U19 telling it the ON/OFF key has been pushed.
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