TLH5699

February 1995

LM903 Fluid Level Detector

General Description

The LM903 uses the thermal-resistive probe technique to

measure the level of nonflammable fluids A low fluid level is

indicated by a warning lamp operating in continuous or

flashing mode All supervisory requirements to control the

thermal-resistive probe including short and open circuit

probe detection are incorporated within the device The cir-

cuit has possible applications in the detection of hydraulic

fluid oil level etc and may be used with partially conduct-

ing fluids

Features

Y

Flashing or continuous warning indication

Y

Warning threshold externally adjustable

Y

Control circuitry for thermal-resistive probe

Y

Switch on reset and delay to avoid transients

Y

600 mA flashing lamp drive capability

Y

Short and open circuit probe detection

Y

70V transient protection on supply and control input

Y

7V – 18V supply range

Y

Internally regulated supply

Y

b

Connection Diagram

Dual-In-Line Package

TLH5699 – 1

Order Number LM903N

See NS Package Number N16E

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A