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Model 173 Probe Type Level Transmitter


  • 4-20 mA, 2 wire, loop powered
  • 10-point linearization for irregularly shaped tanks
  • Digital R.F. Admittance measuring circuitry
  • Intrinsically safe probe circuit
  • Insensitive to process coatings and buildup
  • Simple, two point calibration. No need to empty or fill the tank to calibrate accurately
  • Can be reverse calibrated at will (20 mA=empty tank)
  • Built-in self-diagnostics warn of miscalibration.
  • Choice of integral or remote electronics module
  • Corrosion resistant, NACE #MR-01-75 optional
  • Intrinsically safe electronics design improves safety and lowers cost of installation and maintenance
  • Process pressure as high as 10,000 psig (700 Bar)
  • Process Temperature: -460 to +1500°F (-273 to +800°C)
  • Wide choice of wetted materials includes 316 SS, PTFE,
  • Alloy 20, PVDF, Monel, and ceramics
  • User interface LCD digital display with 4 key input
  • Threaded, flanged, or bracket probe mounting
  • Epoxy sealed electronics module survives harsh environments and area vibration
  • The 173 is essentially 100% repeatable over its range.
  • Built in voltage spike protection, heavy 12 gage terminals


The Model 173 probe style transmitter is used for high reliability measurement of liquid level and interface position. It is insensitive to variations in liquid conductivity, fluid coatings, or solids buildup. The instrument utilizes highly stable crystal references and filters.This allows it to work on narrow ranges and to reliably transmit the level of low dielectric materials. Its sensing probe must be installed in the liquid container so that its active portion passes through the range of fluid elevation points to be measured. The probe is normally inserted vertically down into the liquid from the top of the tank or vessel. Probes can be provided for penetration or mounting at any angle and can be up to 100 feet (33m) long. The electronics module is potted in epoxy for improved reliability under conditions of vibration and corrosion.

It will accurately measure almost any kind of liquid, including: water, oil, gasoline, acid, caustic, soup, milk, gear lube, and antifreeze. It is particularly advantageous when used on fuel oil tanks, cooling tower basins, fruit juice, chlorine storage tanks, irrigation channels, and pharmaceutical reactors. It is also effective for some powdered and granular solids under controlled conditions. The isolated loop powered 4-20 mADC signal is ideal for driving controllers, displays, and supervisory computers.

It will correctly transmit the position of an interface by sensing the ratio of the admittance of the two liquids. Typical interfaces include oil/water, gasoline/acid, and foam/effluent. Interface control is important in crude oil separation, flotation mining, seed oil milling, and fuel tank sediment monitoring. The interface can be accurately detected even though it may be “cloudy” or be carrying a “rag layer.”


The Model 173 utilizes digital admittance technology to measure how much of its sensing probe is covered by the liquid of interest. This is accomplished by generating a radio frequency pulse of energy which travels from the sensing probe to the ground reference (usually the tank wall). The amount of liquid between the two determines how much energy is transferred. The energy flowing (very small and low level in all cases) is a highly repeatable measure of the liquid level or interface position. The amount is integrated and used to produce the 4-20 mADC material elevation signal.


Calibration is simple and easy. The Delta Controls Model 173 can be calibrated using any two levels in the tank. The tank does not have to be completely filled or emptied. You need only change the level to get a required second known elevation. For irregularly shaped tanks, up to 10 calibration points can be entered to linearize the output signal.

Basic Specifications

  • Level range: Dependant on the probe selected, see Application Note # PROB –298 and probe data sheets.
  • Minimum Level Span (“QSU”): 40 Sensing Units
  • Maximum Range (“RSU”): 16,000 S.U.
  • “Zero” Suppression: to 16,000 Sensing Units
  • Output: 4-20 mADC, 2 wire, loop powered, isolated, up to 10-point linearization
  • Loop Supply Voltage Range: 11-35 VDC
  • Max Loop Impedance: 650 ohms @ 24V, 1200 @ 35V
  • Ambient Operating Temperature: -20 to +175°F (+80°C)
  • Process Temperature: -460 to +1500°F (-270 to +810°C)
  • Accuracy and Stability: Within 0.2% of full scale (limited to .05 S.U.)
  • Temperature Effect: Typically less than 0.2″ in water; 0 to +150°F (-18 to 67°C)
Delta Controls Corporation

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