Capacitance Level Control Definitions

ROBERTSHAW CAPACITANCE LEVEL

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Capacitance Level Definitions

High Level Fail Safe (HLFS):

Relay de-Energizes on High Alarm condition. Thus the alarm condition with power failure.  Example: To Keep tank from overfilling with power failure.

Low Level Fail Safe (LLFS):

Relay de_Energizes on Low Alarm Condition. Thus alarm condition with power failure. Example: To Keep pump from running dry and burning up with a ower failure.

Time Delay:

Used for Splashing or wavy processes to prevent cycling on and off.

Response Time:

How fast the unit goes to alarm condition after set point is reached.

C, NO, NC Contacts:

Contacts are normally shown in the non-energized alarm condition – no power, shelf condition.  Relay energizes in non-alarm condition.

POINT LEVEL

ZERO:

This is the SET POINT. Where the desired actuation is to occur.

DIFFERENTIAL:

This is the distance, in Pico-Farads, inches or feet from ZERO to where the RESET is to occur. Sometimes called Deadband or Pump On – Pump Off.

CONTINUOUS LEVEL

ZERO:

The 0% Level point on the sensing probe.

100%:

The full level point on the sensing probe.

SPAN:

The distance in Pico-Farads, from the Zero Level point to the FULL Level Point (100%).

TERMINAL CAPACITANCE:

The Minimum amount of Capacitance present when no product is present in the vessel.

This is:

The Capacitance of the Probe Gland (and sheath and colling extension, if used) PLUS

The Capacitance generated between the probe and the vessel with air as the dielectric. In other words, the absolute minimum value of capacitance generated in that particular probe/vessel installation.

TERMINAL / SPAN RATIO:

The Terminal Capacitance divided by the span capacitance. This ratio must not be exceeded where specified on product specification sheets (all instruments do not have this restriction).

Terminal Adjustment/Zero Adjustment Range/Maximum Zero Suppression:

This is the maximum “Zero Suppression” of the capacitance value at the zero point level in the vessel.  This value cannot be exceeded.

Capacitance Change:

The amount of capacitance difference between ZERO and 100% points in the continuous level measuring instruments; the amount of capacitance difference between product and no product in point level measuring instruments without differential; or the amount of capacitance difference between ZERO and Differential points in Point Level measuring instruments with differential adjustment.

TOTAL CAPACITANCE:

This is the total capacitance value (not capacitance change) with tank of vessel at the 100% level (includes terminal capacitance). This value must not exceed the maximum span of the instrument.

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