Model TPC


Pressure Corrector Add-On Option for Level Measurement in Pressurized Unvented Tanks

The Delta Controls Model TPC works in conjunction with, and connects to the housing of a Series 550 Level Transmitter. The Series 550 head pressure level transmitters measure the height of liquid in a tank by measuring the pressure at the bottom of the tank. That pressure is linearly proportional to the height of liquid above the transmitter sensor in an open tank. Any pressure in the gas space of a closed tank is additive to the pressure measured at the bottom of the tank. The Model TPC corrector senses the gas space pressure and electronically subtracts it from the total pressure sensed by the level sensor located at the bottom of the tank. The formula is:

PTB – PGS = PHD (Which is due to the liquid level in the tank)


PTB = Total Bottom Pressure
PGS = Pressure in gas space (positive or vacuum)
PHD = Pressure at bottom of tank due to liquid height

The bottom and top tank pressures are linked electronically rather than mechanically with a wet leg. The TPC avoids the plugging, condensation, and evaporation problems associated with conventional D/P cell wet legs and impulse piping. The absence of a wet leg also makes a purge system unnecessary when the liquid carries entrained solids. The TPC can also be used to measure the density of a liquid in a vented or pressurized tank. The top sensor is moved down in the tank so that it will always be covered by the liquid. The difference in pressure measured between the two elevations is proportional to the density of the liquid. This setup also allows the elevation position of an interface to be transmitted. Seals, capillaries, purging, air bubbling, etc. are not required.


  • Provides D/P Cell Level Benefits Without Their Problems
  • The Diaphragm Seals And Capillary Tubing Commonly Required By D/P Cells Are Not Needed
  • No Need For A Troublesome "Wet Leg" Reference, No Wet Leg To Get Plugged Or to be Emptied By Evaporation
  • Adds On To A 550 Head Pressure Level Transmitter the Separate Modular Electronics
  • Powered By The Basic 2 Wire Level Loop; Additional Power Supplies, Wires, Etc. Are Not Required
  • An Oil Filled 316-L Or Hastelloy"C"® Diaphragm Protects The Silicon Pressure Sensor Element
  • Piping, Valving, And Installation Is Simplified
  • Can Work Under Vacuum and/or Pressure Conditions
  • Works On Hazardous Materials Where Both Sensing Connections Must Be Through The Top Of The Tank
  • Undisturbed By Agitation, Demisters, Or Heating
  • Can Be Used To Measure Density Of The Liquid
  • Great For Tanks With Gas Blanketing Back Pressure Relief Valves, Or Disc Vents
  • Low Installed Cost And Good Accuracy
  • External To The Vessel Impulse Line
  • Maintenance Is Not Required


  • Service: Used with Delta Controls Models 552, 562, 563, 564, 566, 572, and 592 for measuring level in unvented tanks
  • Action: Corrects for gas space pressure variations
  • Supply Power: None required, works off of the 2 wire level signal loop, Intrinsically safe
  • Protective Devices: Integral voltage and noise suppressers
  • Electronics Location: Mounted in the level transmitter housing, and is part of the module
  • Over Pressure: 2X Range, 35 PSI (2.5 Bar) minimum without damage; 3X Range, 1000 PSI (70 Bar) minimum without rupture
  • Temperature Range:
    • -20 to +220°F (-30 to 105°C) Sensor
    • -20 to +180°F (-30 to 85°C) Electronics Module
    • 30 to +130°F (0 to 55°C) Compensated (Higher Available)
  • Accuracy: ±0.25% F.S. or better
  • Thermal Error: ±0.02% F.S. / °F (0.01% F.S. / °C) maximum
  • Barometric Effect: None
  • Hysterisis: None measurable

Third Party Approvals

  • C.S.A. (Canada); NRTL/C (USA)
  • Intrinsically Safe
  • Explosion Proof
  • Environment Proof
  • 3A Sanitary

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