At present, the patient must be intented by the patient to infuse the bottle, and when the liquid is almost exhausted, tell the doctor promptly. After the operation, patients need to change a few bottles of medicine at night, which causes a large workload for the nursing staff.
We have tried an infusion monitor. When the patient infusion, the small probe is clamped on the liquid hopper of the infusion set. When the drop of the bottle is completed, the liquid level in the liquid hopper drops, and when the liquid level in the liquid hopper drops to a certain value. The monitor sounds an alarm to remind the medical staff to change the medicine. Through experiments, the sensitivity and accuracy are very good.
First, the circuit principleThis design adopts a non-contact sampling method - capacitance method. It is a liquid level sensor consisting of two pieces of copper on the inside of the transparent plexiglass frame, as shown in Figure 1.
When infusion, the infusion set's hopper is sandwiched between two copper sheets. We know that the capacity of a capacitor is related to the medium between the two plates, and the liquid medium is larger than the capacity of the air medium. Thus, the liquid level signal is obtained by measuring the capacitance between the two copper sheets.
Figure 1 is an outer casing made of plexiglass sheets (adhesively formed). The front is open, stuck on the hopper, and the liquid level is directly visible. The capacitance of the two copper sheets is proportional to the level of the liquid. When the liquid level drops, the capacitance decreases, and the voltage measured by the monitor also decreases. When it is less than the set value by amplification and comparison, the speaker emits a warning sound (slight ambulance sound).
The infusion automatic monitor circuit is shown in Figure 2. The non-gate IC1, IC2, IC3 and the resistors R1, R2 and the capacitor C1 form an oscillator to generate an AC oscillating signal. C3 is the capacitor composed of two copper sheets on the inside of the level sensor. The AC signal of the oscillator is rectified by coupling C2 and C3 to the diode VD1 to obtain a DC signal.
The capacity of C3 varies with the liquid level of the liquid, so the size of the DC signal represents the level of the liquid level. The operational amplifier IC4, resistors R4 and R5 form a non-inverting operational amplifier. Due to the low operating voltage of the monitor, the C3 capacity is small and the DC signal is very weak.
Therefore, it is sent to IC5 by about 2 times of IC4 amplification. IC5 is connected to potentiometer RP and resistor R6 as a comparator. The comparator voltage (ie, the alarm voltage) is set by the potentiometer RP. The set alarm voltage is about 800/0 of the full voltage (the voltage generated by the liquid level equal to the upper side of the copper piece is set to the full voltage).
When the liquid is small, the DC signal is also low. When it is lower than the set alarm voltage, IC5 outputs a high potential. It is reversed by IC6 and IC7 (it makes the alarm more accurate, and it is unstable after the experiment, without IC6, IC7 alarm critical point), so that the triode VT1 is turned on. The IC8 is a four-sound music integrated block that is connected to the ambulance music (see Figure 3). VT1 conduction is equal to turning on the IC8 power supply negative.
IC8 causes the speaker BL to emit an ambulance sound. Changing the value of R9 can adjust the size of the speaker sound. VD3 is a Zener diode, which is connected to R7 and C5 as a voltage regulator circuit. The circuit will still operate when the supply voltage drops to 4.1V.
Second, the component selectionThe circuit in the dotted line of Figure 2 is soldered to a small circuit board of 50mm & TImes; 22mm, and the printed circuit board diagram is shown in Figure 4, which is fixed with the liquid sensor housing. It is preferably fixed on the back of the tank sensor housing to form a liquid bucket probe.
The other components are housed in a small box to form a control box for the alarm part of the monitor. This will extend the probe to the control box to 1.2m. The monitor uses two TC4069UBP integrated circuits, and IC1, IC2, and IC3 share one. IC6 and IC7 use another block.
The signal of the liquid bucket probe is very weak and easy to be disturbed. In order to extend the connection between the liquid probe and the control box and reduce the interference, X1, X2 and X3 use a two-core screen to cover the wire, and the shielding layer is to be grounded. connection. The speaker BL uses an ultra-thin inner magnetic type small speaker having a height of less than 10 mm.
X is the earbud jack. Plug in the earplugs and only the guardian can hear the sound. Does not affect the patient's rest. C1 and C2 must use mica capacitors. Shielded wires should be used when the C3 connection cable is greater than 40mm.
Third, debugging Because the probe liquid level sensor is a plexiglass frame, the size processing is not easy to accurately control, and the sensor full potential will not be exactly the same. Now let's take a better example of our debugging for reference.
When the liquid level in the liquid hopper is the same as the height of the copper sheet, the potential at the K1 point is tested. If it is 1000mV. At this time, the potentiometer RP is adjusted so that the voltage at the K2 point is 800 mV. Adjust the liquid level of the infusion set liquid tank; make the liquid level slowly drop, and when it drops to about 80% of the original liquid level, start the alarm.
If the alarm signal of each infusion monitor is sent to the nurse center of the ward, the nurse center can know the infusion of the first number of beds in time.
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