NSC LM1830N Fluid detector Datasheet

LM1830 Fluid Detector
General Description
Features
The LM1830 is a monolithic bipolar integrated circuit designed 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.
Y
Y
Y
Y
Y
Y
Low external parts count
Wide supply operating range
One side of probe input can be grounded
AC coupling to probe to prevent plating
Internally regulated supply
AC or DC output
Applications
Y
Y
Y
Y
Y
Beverage dispensers
Water softeners
Irrigation
Sump pumps
Aquaria
Y
Y
Y
Y
Radiators
Washing machines
Reservoirs
Boilers
Logic and Connection Diagram
Dual-In-Line Package
TL/H/5700 – 1
Order Number LM1830N
See NS Package Number N14A
C1995 National Semiconductor Corporation
TL/H/5700
RRD-B30M115/Printed in U. S. A.
LM1830 Fluid Detector
February 1995
Absolute Maximum Ratings
Output Sink Current
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Supply Voltage
Power Dissipation (Note 1)
20 mA
Operating Temperature Range
b 40§ C to a 85§ C
Storage Temperature Range
Lead Temp. (Soldering, 10 seconds)
28V
1400 mW
b 40§ C to a 150§ C
260§ C
Electrical Characteristics (V a e 16V, TA e 25§ C unless otherwise specified)
Typ
Max
Units
Supply Current
Parameter
Conditions
Min
5.5
10
mA
Oscillator Output Voltage
Low
High
1.1
4.2
Internal Reference Resistor
Detector Threshold Voltage
Detector Threshold Resistance
Output Saturation Voltage
Output Leakage
Oscillator Frequency
8
5
IO e 10 mA
VPIN 12 e 16V
C1 e 0.00 1mF
4
V
V
13
680
10
25
15
kX
mV
kX
0.5
2.0
10
12
V
mA
kHz
7
Note 1: The maximum junction temperature rating of the LM1830N is 150§ C. For operation at elevated temperatures, devices in the dual-in-line plastic package
must be derated based on a thermal resistance of 89§ C/W.
Schematic Diagram
TL/H/5700 – 2
2
Typical Performance Characteristics
Normalized Oscillator Frequency
vs Supply Voltage
Threshold Resistance vs Supply
Voltage
Power Supply Current vs
Supply Voltage
Reference Resistor vs Ambient
Temperature
Detector Threshold Voltage
vs Temperature
Probe Threshold Resistance
vs Temperature
Oscillator VOH and VOL
vs Ambient Temperature
Output Saturation Voltage vs
Output Current
Oscillator Frequency vs
Ambient Temperature
Equivalent Resistance vs
Concentration of Several
Solutions
TL/H/5700 – 3
3
Application Hints
It is possible to calculate the resistance of any aqueous
solution of an electrolyte for different concentrations, provided the dimensions of the electrodes and their spacing is
known.
The resistance of a simple parallel plate probe is given by:
The LM1830 requires only an external capacitor to complete the oscillator circuit. The frequency of oscillation is
inversely proportional to the external capacitor value. Using
0.001mF capacitor, the output frequency is approximately 6
kHz. The output from the oscillator is available at pin 5. In
normal applications, the output is taken from pin 13 so that
the internal 13k resistor can be used to compare with the
probe resistance. Pin 13 is coupled to the probe by a blocking capacitor so that there is no net dc on the probe.
Since the output amplitude from the oscillator is approximately 4 VBE, the detector (which is an emitter base junction) will be turned ‘‘ON’’ when the probe resistance to
ground is equal to the internal 13 kX resistor. An internal
diode across the detector emitter base junction provides
symmetrical limiting of the detector input signal so that the
probe is excited with g 2 VBE from a 13 kX source. In cases
where the 13 kX resistor is not compatible with the probe
resistance range, an external resistor may be added by coupling the probe to pin 5 through the external resistor as
shown in Figure 2 . The collector of the detecting transistor
is brought out to pin 9 enabling a filter capacitor to be connected so that the output will switch ‘‘ON’’ or ‘‘OFF’’ depending on the probe resistance. If this capacitor is omitted,
the output will be switched at approximately 50% duty cycle
when the probe resistance exceeds the reference resistance. This can be useful when an audio output is required
and the output transistor can be used to directly drive a loud
speaker. In addition, LED indicators do not require dc excitation. Therefore, the cost of a capacitor for filtering can be
saved.
In the case of inductive loads or incandescent lamp loads, it
is recommended that a filter capacitor be employed.
In a typical application where the device is employed for
sensing low water level in a tank, a simple steel probe may
be inserted in the top of the tank with the tank grounded.
Then when the water level drops below the tip of the probe,
the resistance will rise between the probe and the tank and
the alarm will be operated. This is illustrated in Figure 3 . In
situations where a non-conductive container is used, the
probe may be designed in a number of ways. In some cases
a simple phono plug can be employed. Other probe designs
include conductive parallel strips on printed circuit boards.
Conductive Fluids
City water
Sea water
Copper sulphate solution
Weak acid
Weak base
Household ammonia
Water and glycol mixture
Wet soil
Coffee
1000 d X
#
c.p A
where A e area of plates (cm2)
d e separation of plates (cm)
c e concentration (gm. mol. equivalent/litre)
p e equivalent conductance
(X b1 cm2 equiv. b1)
Re
(An equivalent is the number of moles of a substance that
gives one mole of positive charge and one mole of negative
charge. For example, one mole of NaCl gives Na a a Clb so
the equivalent is 1. One mole of CaCl2 gives Ca a a a 2Clb
so the equivalent is 1/2.)
Usually the probe dimensions are not measured physically,
but the ratio d/A is determined by measuring the resistance
of a cell of known concentration c and equivalent conductance of 1. A graph of common solutions and their equivalent
conductances is shown for reference. The data was derived
from D.A. Maclnnes, ‘‘The Principles of Electrochemistry,’’
Reinhold Publishing Corp., New York., 1939.
In automotive and other applications where the power
source is known to contain significant transient voltages, the
internal regulator on the LM1830 allows protection to be
provided by the simple means of using a series resistor in
the power supply line as illustrated in Figure 4 . If the output
load is required to be returned directly to the power supply
because of the high current required, it will be necessary to
provide protection for the output transistor if the voltages
are expected to exceed the data sheet limits.
Although the LM1830 is designed primarily for use in sensing conductive fluids, it can be used with any variable resistance device, such as light dependent resistor or thermistor
or resistive position transducer.
The following table lists some common fluids which may
and may not be detected by resistive probe techniques.
Non-Conductive Fluids
Pure water
Gasoline
Oil
Brake fluid
Alcohol
Ethylene glycol
Paraffin
Dry soil
Whiskey
4
Typical Applications VCC e 16V
FIGURE 2. Application Using External
Reference Resistor
FIGURE 1. Test Circuit
TL/H/5700 – 4
Output is activated when Rp is approximately greater than (/3 RREF
FIGURE 3. Basic Low Level Warning Device
with LED Indication
FIGURE 4. Direct Coupled Applications
5
Typical Applications VCC e 16V (Continued)
Low Level Warning with Audio Output
High Level Warning Device
TL/H/5700 – 5
The Output is suitable for driving a sump pump
or opening a drain valve, etc.
6
7
LM1830 Fluid Detector
Physical Dimensions inches (millimeters)
Molded Dual-In-Line Package (N)
Order Number LM1830N
NS Package Number N14A
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