Model 512

SKU: 512

Conductance Level Switch, Two Relay

Model 512 – Dual Channel

Model 512 – Single Channel

Model 512 – Quad Channel


  • Reliably detects conductive solids or liquids
  • Circuit board is plastic coated for protection against moisture and corrosion DPDT relay is sealed for high reliability
  • Unaffected by conductive buildup on the probe
  • Actuation setpoint resistance is adjustable to prevent false switching
  • 2 second time delay is basic, 1-60 seconds adjustable is optional
  • 4X hoseproof housing is basic
  • Low level sensor voltage for safety
  • AC signal protects sensing probe life
  • Intrinsically safe probe is optional


  • Relay: 5 amps @ 120 or 240 VAC, 50/60 Hz, 4 amps @ 28 VDC; DPDT; (SPDT when wired for differential)
  • Supply Power: 120 or 240 VAC, 5 VA
  • Operating Temperature: -20°F to +180°F (-30 to +85°C), (PVC housing limit is 140°F, 61°C)
  • Response: 2 seconds fixed time delay (0-60 seconds adjustable optional)
  • Basic Input: Equivalent adjustable from 100 to 35,000 ohms
  • Solution Conductivity: Potable water to strong acids; carbon solids


The relay switches when the conductive material makes an electrical connection between the sensing probe and ground return. The sensing rod(s) length is selected so that the rod tip is at the elevation where switching is required. The instrument only has a low AC voltage on the sensing probe, even under conditions of an open probe circuit. Many competitive devices require hundreds of volts on the probe. This can be extremely dangerous, particularly when used on an open tank or pit application.


The switch station actuates its relay when a small electrical current flows from its sensing probe to the vessel wall or to another probe being used for ground return. A low voltage AC signal is applied between the sensing probe and ground. The very small current is conducted between the two when the process liquid touches the sensing probe. This current flow is sensed by an electronics network which actuates the output relay.

On/off differential control is accomplished by using two sensing probes, one of which is longer than the other. The relay is actuated when the liquid level touches the upper probe. The relay actuation disconnects the upper probe and connects the lower probe to the measuring circuit input. The unit is then "latched in" through the lower probe/liquid/ground connection and remains actuated until the liquid level drops below the lower probe. The relay then deactuates, and the upper probe is reconnected to the measuring circuit input.

A single conductive return path is common to all stations. This path can be a probe, metal tank, earth ground, etc.

Probe Specifications

  • Working Pressure: -15 to 1,500 PSIG (-1 to 100 BAR)
  • Process Temperature: -50 to +900°F (-45 to +500°C)
  • Process Connection: NPT,ANSI Flange, Sanitary Flange, BPT, DIN, Wall bracket, Custom designs
  • Wetted Materials:
    • Bodies and Electrodes: 316 S.S., Hastelloy® "C"; Titanium, Monel, and others.
    • Jackets and Cable Insulation: PVC, PTFE
    • Housings: PVC, Fiberglass, Aluminum, S.S.
    • Seals: Viton® "O" rings, PTFE packing; ceramic and glass packing
  • Insertion Lengths (basic):
    • Rods: 1 inch to 20 feet (25 to 6100 mm)
    • Cables: 6 inch to 1,500 feet (150 to 500 M)
  • Solution Conductivity: Potable water to strong acids, and carboneous solids
  • Junction Housings: Type 4X Hoseproof for wet and corrosive areas, stainless steel fasteners; Explosionproof in aluminum or stainless steel material
  • Intrinsically Safe Probe Barrier For Explosion Hazard Areas: Stahl #9001/02-412-095-10 or equivalent may be used
  • Custom configurations and materials; contact Delta Controls

Conductive Buildup

The Delta Controls Model 512 / 513 / 514 does a better job on fluids that leave conductive deposits than do most other types of level switches. Many process fluids carry entrained solids, which accumulate on any surface that they contact. These deposits usually remain conductive after the fluid has dropped off of the probe and commonly continue to collect until the physical size of the buildup mass is quite large. The Model 512/513/514 will continue to operate through a conductive buildup because when the fluid rises and contacts the buildup mass, the sensing current flow, through the conductive buildup, through the fluid, and on to ground return. The sensing probe should enter the vessel vertically from the top. This vertical orientation prevents the collected buildup from bridging across the rod insulation to the tank wall ground, which could cause the Models 512 / 513 / 514 to be continuously activated.

Fluids/Solids Sensed

This unit will sense the presence of water and almost any water based compound or mixture. A solution having 10% or more free water is usually adequate for operation. Typical examples are: acid, tap water, sodium hydroxide, brines, and mine water. Most carbons and many carbon bearing solids are conductive and can be detected by the Models 512/513/514. These solids may be in the form of powders, granules, or lumps. Typical examples are: coal, coke, graphite, and carbon black.

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