Model 780 - Liquid Interface Measurement System

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DESCRIPTION

The superior design of the INVALCO Interface Measurement System offers reliable, precise control of gas/liquid or liquid/liquid interface level. Carefully matched electronic assemblies with probe components combine to provide a measurement system for the most demanding applications. A wide variety of standard features and ease of installation give the IMS 780 the flexibility necessary for optimum performance. The Interface Measurement System (IMS) has been carefully designed for dedicated interface control and surpasses all other multipurpose devices.

Specifications

Operating Temperature	-20°F to 160°F
Probe Temperature	250°F Maximum
Power	110/220 VAC, 50/60 Hz or 24 VDC 6 watts
Maximum Working Pressure	350 psig @ 100°F
Outputs	Continuous - 4 to 20 mA Relay Contacts-DPDT, 10 Amps at 115 VAC non-inductive
Fail-safe Mode	Low Level
Sensitivity	+/- 0.3 pf
Response Time to a dk Change	0.75 seconds or less.
Enclosures	Weatherproof - NEMA 4X Explosion-proof - Class 1, Groups C and D.
Adjustable Time Delay For Relay Closure	0-55 Seconds
Certification for Use in Hazardous Areas	Probe is certified for use with either W.P. or X.P. housed control unit. X.P. housed control unit is certified for use in hazardous areas. cUL and UL approved File: E215164 Type: Class 1, Groups C & D

FEATURES

Excellent Sensitivity and Repeatability - means precision control even with difficult applications.
Non-Fouling Probe - for continuous, reliable use.
Convenient Operator Interface - provides visual status indication and greatly reduced set-up time.
Individually Adjustable Dual Outputs with Time Delay - allows the flexibility needed to change and customize control of your system.
Approved for use in hazardous locations. cUL and UL approved. Class 1 Groups C & D.
110/220 VAC or 24 VDC 6 watts.
Probe length variations available. Consult factory. Standard probe designs and lengths shown on page 3.

THEORY OF OPERATION

The INVALCO IMS Model 780 works on the principle of measuring an electrical value, called capacitance, that exists from itʼs probe to ground. It does this by measuring the dielectric constant (dk) value of the material surrounding the probe and the distance from the probe to the nearest, and largest, ground plane which normally is the conductive water below the oil/water interface. The capacitance value will increase if the material dk increases, or if the water moves closer to the probe. Conversely, the capacitance will decrease if the material dk decreases, or if the water moves away from the probe. The main, dominating, factor is the distance from the probe to the water which thereby allows the IMS 780 to be a superior level indicator/control device. The unit is sensitive to extremely small changes (+/- 0.3 pf) and with a horizontally mounted probe, can be set to measure a clean interface as much as 24 inches away, depending upon fluid characteristics.

The use of capacitance to detect interface levels in many applications has always been complicated by the electrical conductivity of the fluids and the buildup of conductive materials on the probes. These cause changes in conductivity which are mistaken for changes in capacitance, resulting in a misinterpretation of the interface level, or instrument failure. Interference caused by changes in conductivity are virtually eliminated by the use of high frequencies in the INVALCO IMS detection circuit design. Normally, high frequency requires the use of special cable (coaxial) to carry the signal which introduces other complications. The high frequency oscillator and detection circuitry in the INVALCO IMS are mounted in the probe and overcome the need for special cable. The control unit can be remotely mounted up to 500 feet away.

APPLICATIONS

Petroleum and Gas
- Separators
- Heater Treaters
- Desalters
- Free-water Knock-out

Other Industrial Liquid Processing
- Storage Tanks
- Extraction Units
- Separation Equipment

IMS MODEL 780

The Model 780 is designed to provide both a continuous (throttling) and snap-acting (on/off) output mode.

The snap-acting selector is a 10-position switch. The zero position is normally used when the Model 780 is used to detect a gas/liquid interface. Positions 1-9 are used to detect ever-increasing concentrations of water-in-oil.

Position 1 is nearest 100% oil, position 9 is nearest 100% water.

The Model 780 is also capable of developing a 4-20 mA throttling output which is particularly effective when applied to free-water knock-outs, treaters (crude oil dehydrators), wash tanks (gun barrels), skim tanks, three-phase separators, and other process vessels where an interface level must be maintained at a reasonable constant level.

The throttling selector has four positions marked 1, 2, 3, and 4. These positions correspond with the instruments overall span with respect to the water content of the oil at the interface.

Though actual water concentrations corresponding to the four positions vary with the different characteristics of oil and water, the general ranges follow:
Position 1 - 0-25% Water
Position 2 - 0-50% Water
Position 3 - 0-75% Water
Position 4 - 0-100% Water

INSTALLATION AND START-UP

The Model 780 probe may be installed horizontally, vertically, or at an angle. A horizontally mounted probe will be able to detect an interface further away than a vertical or angle mounted probe due to the area of the probe which is parallel to the interface. A horizontally mounted probe will have the entire length and width of the probeʼs electrode parallel to and “looking down” to the interface while a vertical, or angle mounted probe will have only the circular area of the end of the probe electrode “looking down” to the lower interface. Normally a horizontally mounted probe is used when it is desired to control an interface below the probe while a vertical, or angle mounted probe is used when it is desired to control the interface on the probe electrode proper.

A packing gland on the probe allows it to be installed into, or removed from, a vessel without having to depressurize , or drain down, the vessel.

A single screwdriver calibration potentiometer is adjusted to set up the instrument for level control or interface control. Then simply turn the two knobs on the face of the 780 to get the desired relay and 4-20mA outputs. Then turn the time delay knob to eliminate any relay chatter caused by ripples, or waves, on the interface surface.

ADDITIONAL INFORMATION

Note: Dimensions at images – Inches to the nearest tenth (millimeters to the nearest whole mm), each independently dimensioned from respective engineering drawings.