LM Fluid Detector. The is a monolithic bipolar integrated circuit designed for use in fluid detection systems The circuit is ideal for detecting the presence. LM datasheet, LM circuit, LM data sheet: NSC – Fluid Detector, alldatasheet, datasheet, Datasheet search site for Electronic Components and. LM Datasheet, LM PDF, LM Data sheet, LM manual, LM pdf, LM, datenblatt, Electronics LM, alldatasheet, free, datasheet.

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Manufactured by National Semiconductors, the LM can detect the presence or absence of polar fluids. Circuits based on this IC requires minimum number of external components and AC signal is passed through the sensing probe immersed in the fluid.

Usage of AC signal for detection prevents electrolysis and this makes the probes long lasting.

The circuit of a low liquid level indicator with LED is shown above. Capacitor Ct sets the frequency of the internal oscillator. With the give value of C1 the frequency will be around 6KHz.

Capacitor Cb couples the oscillator output to the probe and it ensures that no DC signal is applied to the probe. The circuit detects the fluid level by comparing the probe to ground resistance with the internal reference resistor R datasjeet. When the probe to ground resistance goes above the R ref the oscillator output is coupled to the base of the internal output transistor making it conducting. The LED connected to the collector between pin 12 and Vcc is driven.

There is dataxheet problem in driving the LED using AC signal and this method is very useful when it comes to use a loud speaker as the indicator. Loud speakers can be datasbeet only by using AC signals and a DC signal will not produce any datawheet out of the speaker. The circuit diagram of a liquid level indicator using loud speaker at its output is shown below.


The circuit is similar to the first circuit except that the LED is replaced by a loud speaker and the load current limiting datasheef is changed from 1. Some time there may be situations when the fluid resistance probe to ground do not match with the 13K internal reference resistor. In such cases there is option to avoid the internal reference resistor and an external reference dxtasheet of your choice Rx in the circuit can be employed. The oscillators output is directly available at pin 5 and the Rx connects the oscillator output to the probe through the blocking capacitor.

(PDF) LM1830 Datasheet download

Dataheet circuit diagram for the above said scheme is shown below. A method for activating a relay when the liquid level exceeds a predetermined level is shown here.

DC voltage is required for driving the relay and AC voltage cannot be used datasehet just like what we did in the case of Datassheet and speaker.

Pin 9 of the IC can be used to solve this problem. A capacitor connected from this pin to ground will keep the internal output transistor steadily ON whenever the probe resistance goes higher than the reference resistor.

Dataeheet transistor Q1 is connected to the collector of the internal transistor. The load that is the relay is connected at the collector of Q1. When the probe is not touching the water it equal to an open circuit situation and surely the probe resistance will be many M ohms and it is greater than the R ref 13K. The internal transistor will be switched ON and Q1 whose base is connected to the collector of the internal transistor will be in OFF condition keeping the relay inactive.

LM datasheet & applicatoin notes – Datasheet Archive

When the reverse scenario occurs fluid level touches the probe the internal transistor is switched OFF and this in turn makes the transistor Q1 ON resulting in the activation. The load connected through dstasheet relay whether pump, lamp, alarm, solenoid valve or anything is driven. Resistor R3 limits the collector current of the internal transistor while resistor R4 provides protection to the IC from transients.


The probe used here can be any metal rod with size and shape of your choice.

Datasheet «LM1830»

The tank must be made of metal and it should be properly grounded. For non metal tanks fix a small metal contactor at its bottom level and ground it.

The probe must be placed at the level you want to monitor. You may see the circuit if you are interested. Hi Challa it is meant for normal water, hence can be used for our domestic use to control over head tank water level. How could I use this circuit to control the Digital input on a microcontroller?

Hi Rohit Pin No 5 is oscillator out put for external reference resistance. You have to connect the tweeter between Pin No12 and Vcc through suitable resistance. Please refer dwtasheet the second circuit above. Your email address will not be published. Liquid level indicator admin October 12, 11 Comments.

LM (NSC) PDF技术资料下载 LM 供应信息 IC Datasheet 数据表 (8/8 页)

LM based liquid level indicator circuit. Low liquid level indicator LED. Low liquid level warning audio. Level indicator using external reference resistor. High liquid level activated switch. Previous post Next post. You may also like: Hai, Can it be used for Water level indicator in a Over head Tank.

Achei fantastico o site. Atenciosamente… Washington Souza Gomes. Hi, can this sensor circuit be used to detect diesel fuel? Leave a Reply Cancel reply Your email address will not be published.