User manual

Model: 2100 &2300 Series
2100UM22.DOC Rev: 2.2
- 18 -
4.0 OPERATION
IN THE FOLLOWING TEXT A MENU WILL BE DISPLAYED AS A PATH. FOR EXAMPLE THE
AUTOCAL MENU: [CALIB\ 1]. (CALIB key then 1 for AUTOCAL).
SETTINGS MENU: [SETUP\3] (SETUP key then 3 for SETTINGS).
The 2000 Level Monitor uses a high precision and highly repeatable RF technique to measure
capacitance, which in turn is used to calculate level. The capacitor formed by the level probe (usually
mounted vertically into the vessel) and a ground reference (metallic vessel wall or probe shield for
concentrically shielded probes) changes its capacitance in proportion to the level of the material in
the vessel. In addition, the capacitance is directly proportional to the dielectric constant of the
material in the vessel and inversely proportional to the distance between the probe and the ground
reference. In other words, THE GREATER THE DIELECTRIC, OR THE SMALLER THE GAP
BETWEEN THE PROBE AND THE GROUND REFERENCE, THE HIGHER THE MEASURED
CAPACITANCE AND THE GREATER THE CHANGE OF CAPACITANCE AS THE LEVEL
CHANGES. The dielectric constant is a physical property of matter and is different for different
materials. Water has a dielectric constant of 80 as compared to 3 for most oils. Therefore, water
gives a much higher change in capacitance then oils which makes measuring the level of water much
more precise as compared to oils. For a linear response, the CAPACITANCE LEVEL PROBE MUST
BE PARALLEL TO THE GROUND REFERENCE. The closer the distance between the probe, the
greater the change in capacitance as the level changes. This may be used to advantage when
measuring materials which have a low dielectric, and which, therefore give a low change of
capacitance as the level changes. Arjay’s method of measuring capacitance gives better than 0.1pF
resolution for typical applications.
All Level-Ease 2000 Series Controllers and Transmitters are intelligent and can perform a number of
tasks simultaneously (multitasking software). This means that even while in another menu, the
capacitance is always be measured in the background. For example if the Filter value is being set in
the SETTINGS submenu (SETUP\SETTINGS menu), the level value, relay alarms and mA outputs
are still being updated. This is important since keypad entries are typically slow and sometimes an
operator might forget to return the unit to the normal DISPLAY menu: in this case Alarm relays and
mA output are still updated. In some menus however, the mA output and or the Alarm Relays are not
updated on purpose; for example while in the calibration menu, the unit assumes that the unit is being
calibrated and so the calculated level may be erroneous. In this case, the mA and Alarm Relays are
set to the inactive states.
Periodically, (every 5-10 seconds) the unit does a self-diagnostic. If major errors are found they are
displayed on the LCD. These error messages take precedence over the level information in the
DISPLAY menu ONLY. All other menus may be entered and parameters viewed or changed. In
case of errors, this allows the user to enter the DIAGNOSTICS menu and check the capacitance or
frequency etc.
4.1 DISPLAY MENU [DISP]
This is the default or normal operating screen. It shows:
LEVEL
3454 lbs
50.3%

The 2nd line shows the vessel capacity in engineering units. The value is calculated as level % times
Full Scale Engineering Units value.
The 3rd line shows the vessel capacity in percent fill.
The 4th line shows a bar graph of the level in percent fill. The resolution is 5%.