GB2169082A

GB2169082A - High frequency electrode type low-level alarm for drip-feed injection

Info

Publication number: GB2169082A
Application number: GB08530707A
Authority: GB
Inventors: Shang-Jing Lin
Original assignee: TYAN RUNG IND Ltd CO
Current assignee: TYAN RUNG IND Ltd CO
Priority date: 1984-12-13
Filing date: 1985-12-13
Publication date: 1986-07-02
Also published as: GB8530707D0

Abstract

A high frequency electrode type low level alarm for drip-feed injection comprises a detecting electrode 101, a high frequency oscillator 102, a comparator 103, a current amplifier 104, an alarm 105, and a DC Source 106. The electrode 101 is positioned at a predetermined level on the outside of a container of injection liquid and when this level is reached by the liquid the electrode causes a change in high frequency load impedance on the oscillator which in turn varies the amplitude of oscillation. The oscillator current consumption through resistor R101 changes and comparator 103 outputs a signal to trigger the alarm (105) whenever the injection liquid reaches the predetermined low level. A second high frequency oscillator 107 having substantially the same design as the first may be connected to the other input of the comparator for compensation of the influence of environmental variations. <IMAGE>

Description

SPECIFICATION High frequency electrode type low level alarm for drip-feed injection The present invention relates to a high frequency electrode type low-level alarm for dripfeed injection, the main object of which is to eliminate the need for frequent patrols to inspect whether the injection liquid has reached a low level requiring a renewal of supply. The patrol and inspection is quite a tedious job for the doctor or nurse in order to assure the constant supply of drip-feed injection liquid, and negligence will cause serious trouble which may mean a matter of life and death of the patient.

The present invention aims to provide an automatic low-level alarm system which is effective and economical, reusable, and does not contaminate the liquid being supplied.

According to the invention, there is provided a high frequency electrode type low level alarm for drip-feed injection, comprising: a detecting electrode, a high frequency oscillator, a comparator, an alarm, and a DC Source, in which the detecting electrode is arranged to be attached to the outside wall of an injection liquid container at a predetermined low level point, whereby the actual liquid level as sensed by the electrode, when higher or lower than the low level point, gives a lowering or increase of the high frequency load impedance applied to the oscillator which in turn causes the weakening or strengthening of the oscillation thereof to cause an output signal of the comparator to trigger the alarm as the low level point is reached.

Some embodiments of the invention will now be described by way of example and with reference to the annexed drawings, in which: Figure 1 is a circuit diagram of a preferred embodiment of the present invention; and Figure 2 is a circuit diagram of a second embodiment of the present invention. The second circuit diagram resembles generally that of Fig. 1, except that a further high frequency oscillation circuit for compensation is connected to another input terminal of the comparator.

Now referring to the accompanying drawings, in the circuit diagram of Fig. 1, an electrode 101 is disposed on the outside wall of a glass container holding the injection liquid, at a point X, defining the low level, i.e. the point where drip-feed liquid is to be renewed.

When the actual level is lower than X,, the high frequency impedance Z0 sensed by the electrode 101 is comparatively high, and when the level is higher than XO, the high frequency impedance Z0 will be lower. In other words, when there is sufficient liquid in the container or when the level is higher than the predeter mined level X,, since electrode 101 measures through the liquid, in the high frequency circuit 102, the impedance on point A will drop and the signal on point A is weakened, which in turn weakens the positive feedback signal through the variable condenser VC-101. The self-exciting high frequency oscillator 102 is pre-adjusted to an unstable state, and oscillation ceases or is weakened through the above said influence.Owing to the characteristic that the consumption of current is influenced by the intensity of oscillation, the current passing through resistor R101 is varied and the voltage on point B is hence changed to achieve the purpose of the detection. Therefore, when the oscillation ceases or is weakened, due to the increasing of current th voltage on point B is lowered and the voltage signal on the positive terminal input of the comparator 103 is lower than that of a preset reference set by variable resistance VR101, resulting in no output from the comparator 103 and so alarm 105 remains in a silent condition.On the contrary, when the liquid level is lower than X,, there is no liquid facing the electrode 101, the impedance on point A rises, the positive feedback signal on point A through VC-101 increases in strength and oscillator 102 starts or strengthens its oscillation. The voltage on the input positive terminal of comparator 103 becomes higher than that of the preset reference, and a signal is output from the comparator 103, through current amplification transistor Q102, and the alarm 105 is triggered to response.

The above said high frequency oscillator 102 is a self-excited type having collector/ base feedback and a frequency in the range from 250 to 450 MHz. Variable condenser VC-101 connected to the base of transistor Q101 is adjustable to vary the positive feedback from point A to the base of transistor 0101. Since it is a low power oscillator, the power required is quite small and no radiation problem exists. The characteristic of consumption of current vs the strength of oscillation is utilized, whereby the liquid level can be accurately detected through the voltage change on point B with the aid of a comparator 103.

The circuit is powered by battery 106.

The design of the second embodiment as shown in Fig. 2 takes further environmental factors, namely temperature and humidity, into consideration, to facilitate the application un der more specific conditions without being influenced and accurate detection results.

Since a high frequency oscillator 107 resembl ing the oscillator 102 as shown in block 102 of Fig. 1 is further connected to the negative input terminal of the comparator 103, when the temperature and/or humidity in the envi ronment varies, since the high frequency oscil lators 102, 107 connected to the respective input terminals B and C of the comparator 103 are substantially of the same design, these two terminals are under the same influ ence of environmental factors, and the effects on terminal voltage are compensate and counterbalanced at the output of the comparator 103. Therefore the accuracy of level detection is free from the influence due to variation of temperature and humidity.

Claims

1. A high frequency electrode type low level alarm for drip-feed injection, comprising: a detecting electrode, a high frequency oscillator, a comparator, an alarm, and a DC Source, in which the detecting electrode is arranged to be attached to the outside wall of an injection liquid container at a predetermined low level point, whereby the actual liquid level as sensed by the electrode, when higher or lower than the low level point, gives a lowering or increase of the high frequency load impedance applied to the oscillator which in turn causes the weakening or strengthening of the oscillation thereof to cause an output signal of the comparator to trigger the alarm as the low level point is reached.

2. A high frequency alarm according to claim 1, wherein the current consumption of the oscillator passes through a resistor to give a voltage drop, and the variation of the current as the oscillation weakens or strengthens causes a voltage change, in response to which the output signal of the comparator serves to trigger the alarm.

3. A high frequency alarm according to claim 1 or 2, wherein the high frequency oscillator is coupled to one input of the comparator and a second oscillating circuit of substantially the same design as the high frequency oscillator is connected to the other input terminal of the comparator for compensation of environmental variations of temperature and humidity.

4. A high frequency electrode type low level alarm for drip-feed injection, substantially as hereinbefore described with reference to the accompaying drawings.