MODEL 70A RESISTANCE SENSING POWER RELAYS
MODEL 70A RESISTANCE SENSING POWER RELAYS
•Operates when the input resistance drops below the trip point (or reverse mode).
- Choose from 3 adjustable trip point ranges of 20 megohms, 100 megohms, or 40k ohms.
- Useful for sensing presence of moist solids, slurries, chemicals, liquids, water, ice, etc.
- Suggested applications include storage tank level controls, sump pump control, ice bank control, feed water control, livestock, feeders, protective control systems, alarms, interface, etc.
OPERATION IS SIMPLE
Model 70A Resistance Sensing Power Relays are operated by a change of input resistance, usually detected by (but not limited to) exposed electrodes. Their operation is quite simple . . . when the input resistance drops below the trip point, the relay circuit is energized... when the input resistance rises significantly above the trip point, the relay circuit is de-energized. By means of a simple wire connection on the terminal strips, the control can be operated in a “fai1-safe” mode; i.e. relay normally operated but dropped out on probe contact or loss of power.
TYPICAL APPLICATIONS
Typically, these control devices might be used with exposed electrodes to detect the presence of a wide variety of moist solids, liquids, chemicals, or slurries in a storage tank or bin; to detect ice formation; to detect the presence of an unwanted substance in a protective control system; or other applications where the detection of a change of resistance is desired. Model 70A is available with your choice of a 40k ohm, 20 megohm, or 100 megohm trip point. The 20 megohm trip point would be suggested for use with ores, pellets, granules, or other moist solids; the 100 megohm trip point for certain dry materials; the 40k ohm trip point for water, condensation, and other liquids.
SPECIAL FEATURES
A sensitivity control on the Model 70A permits a moderate adjustment of the actual trip point to provide closer control in more critical applications. They are also available with or without a plug-in electro-mechanical power relay; or with a solid-state power relay for conventional switching of any load or “zero-voltage” switching of resistive loads.
EASY AND SAFE TO USE
Resistance Sensing Power Relays are completely solid state and have no moving parts except the electromechanical power relay if specified. The resistance sensing input circuit is isolated from other circuitry, operates with less than 16 volts on the electrodes, and uses alternating current on the 40k ohm model to prevent damage from electrolytic action. See specifications on page 2 of this bulletin.
