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The Math Behind It . . .
What Is Capacitance?
Capacitance is expressed as the ratio of the electric charge on each conductor to the potential difference (i.e., voltage) between them.
Applying The Math To Level Control . . .
With level transmitters, the output signal in milliamps is dependent on the capacitance formula :
Dielectric Constant x Area of Parallel Plates ÷ Distance Between Parallel Plates or C = KA / D
where the dielectric constant “K” is a value greater than 1. The value “A” is dependent on the diameter and length of the level probe. The value “D” is the distance from the probe to the tank wall, ground reference probe or concentric tube. Consequently, capacitance (C) and the resultant mA output increases as the dielectric constant increases, the probe diameter and length increases, and the distance from the probe to tank wall (ground probe or tube), decreases.
Continuous Level Transmitters + Temperature!
MLST And MLXT-4220
continuous level transmitters are for sanitary and industrial level transmitter applications. A capacitance level transmitter provides a continuous 4-20mA, 20-amA, 1-5VDC or 5-1VDC analog output proportional to the material level in any shaped tank. They can be used for conductive, non-conductive liquids and moist granular solids.
MLST and MLXT - TEMP - 4220’s
are combination continuous level transmitters and temperature transmitters for sanitary and industrial applications. In addition to having all of the standard specifications, they provide 2 separate 4-20mA outputs measuring level and temperature with one probe and one tank connection. Temperature ranges from -100˚ to 1,000˚F.
MLST Sanitary Models
Conforms to NEMA Type 4, 4x, 12 and 13 waterproof and corrosion resistant. Constructed with 14 gauge 304 s.s.
MLXT Industrial Models
Conforms to Class I Groups C & D, Class II Groups E, F, & G and Class III suitable for wet locations. Applicable Standards : Nema 7, 9 and 4x.
Common Features
Applies To Both Sanitary And Industrial Models
• Resolution to better than 1 part in 10,000
• Accuracy and repeatability to less than 0.1% of span
• Microprocessor based capacitance level transmitters with on
board digital to analog conversion assuring negligible output
current error of 0.003%
• Linearity of better than 0.003% over industrial temperature
range of -20˚F to 160˚F
• Designed with most up to date surface mount, integrated
circuits and components
• Standard range of 0.0001 picofarads to 15,000 picofarads
allowing the 4220 to span 4-20mA over 1 inch of water,
(high sensitivity) or hundreds of feet of water (low sensitivity)
• Non interacting zero and span
• Cancel Coat™ circuitry and superior resolution eliminate the
readout errors cause by conductive coatings on the continuous
level controls sensing probe
Approved & Certified : UL, CSA & 3A
