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 LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Europe Fax: (a49) 0-180-530 85 86 Email: cnjwge @ tevm2.nsc.com Deutsch Tel: (a49) 0-180-530 85 85 English Tel: (a49) 0-180-532 78 32 Fran3ais Tel: (a49) 0-180-532 93 58 Italiano Tel: (a49) 0-180-534 16 80 National Semiconductor Hong Kong Ltd. 13th Floor, Straight Block, Ocean Centre, 5 Canton Rd. Tsimshatsui, Kowloon Hong Kong Tel: (852) 2737-1600 Fax: (852) 2736-9960 National Semiconductor Japan Ltd. Tel: 81-043-299-2309 Fax: 81-043-299-2408 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.