When the microprocessor commands the mechanism to pump, the camshaft begins to rotate, thus controlling the following pump cycle:
1.The inlet valve closes.
2.In synchrony with the expulsor moving down to compress the tubing, the outlet valve opens, expelling 0.050 ml of fluid (or 0.100 ml of fluid with a
3.The outlet valve closes.
4.The inlet valve opens as the expulsor is retracted, causing fluid from the reservoir to again fill the pump tubing segment.
5.The camshaft rotation stops after half a revolution and the cycle is completed.
Pumping Characteristics
If the fluid path to the patient becomes blocked, the pump tubing will expand as pumping occurs. When there has been an amount of inflation corresponding to 124 ± 62 kPa
(1.24 ± 0.62 bar, 18 ± 9 psi), the occlusion analog sensor trips, whereupon the microprocessor stops the pump mechanism and issues visual and audible alarms. Thus the maximum pressure which can be developed is 186 kPa (1.86 bar, 27 psi).
To deliver the amount of drug specified by the parameter settings, the pump’s microprocessor
causes the pump mechanism to deliver 0.05 ml (or 0.1 ml with a
Mechanism activations per hr
=20 ml per hr/0.1 ml per activation
=20/0.1
=200
Time (seconds) between activations
=3600 sec per hr/number of activations per hr
=3600/200
=18
| Rate | Volume |
| (ml/hr) | Resolution (ml) |
|
|
|
Cassette or | 0 - 3 | 0.050 |
Admin Set | 3.1 - 125 | 0.100 |
|
|
|
Hi Vol | 0 - 3 | 0.100 |
Admin Set | 3.1 - 350 | 0.200 |
The microprocessor uses its timer circuits to accurately time the 18 seconds (in this ex- ample) between mechanism activations. The timebase accuracy is ultimately determined by the 3.6864 MHz quartz crystal oscillator.
Motor | Camshaft |
Pump Housing | Lock Button |
Expulsor |
|
Occlusion Sensor | Latch Button |
| |
Cassette Hinge |
|
Pump Tubing
Pressure Plate
Inlet Valve
Outlet Valve
Figure 7. A simulated pumping mechanism in a
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