TLH5700

February 1995

LM1830 Fluid Detector

General Description

The LM1830 is a monolithic bipolar integrated circuit de-

signed for use in fluid detection systems The circuit is ideal

for detecting the presence absence or level of water or

other polar liquids An AC signal is passed through two

probes within the fluid A detector determines the presence

or absence of the fluid by comparing the resistance of the

fluid between the probes with the resistance internal to the

integrated circuit An AC signal is used to overcome plating

problems incurred by using a DC source A pin is available

for connecting an external resistance in cases where the

fluid impedance is of a different magnitude than that of the

internal resistor

When the probe resistance increases

above the preset value the oscillator signal is coupled to

the base of the open-collector output transistor In a typical

application the output could be used to drive a LED loud

speaker or a low current relay

Features

Y

Low external parts count

Y

Wide supply operating range

Y

One side of probe input can be grounded

Y

AC coupling to probe to prevent plating

Y

Internally regulated supply

Y

AC or DC output

Applications

Y

Beverage dispensers

Y

Radiators

Y

Water softeners

Y

Washing machines

Y

Irrigation

Y

Reservoirs

Y

Sump pumps

Y

Boilers

Y

Aquaria

Logic and Connection Diagram

Dual-In-Line Package

TLH5700 – 1

Order Number LM1830N

See NS Package Number N14A

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A