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6 Setup with the integrated display and adjustment unit
ply and measurement data are transmitted
over the same two-wire cable. This mode is
provided for connection of measuring trans-
ducers without separate operating voltage
(sensor in two-wire version).
•
In passive mode, the sensors are not
powered, only the measurement value
is transmitted. This mode is provided for
connection of transmitters with their own
separate operating voltage (sensors in four-
wire version).
→
Set the function switch to position [F] and
select the suitable mode with the [+/-] keys.
Save your settings by pushing both keys
simultaneously.
Offset correction
When a pressure transmitter is used, an offset
correction should be carried out first. These
instruments are factory-set in a certain position.
If the pressure transmitter is now mounted in a
different position, its measuring range is shifted
slightly. The zero point is readjusted by carrying
out the offset correction in uncovered (unpres-
surised) condition. The complete measuring
range will be shifted by the deviating amount.
1. Make sure that the pressure transmitter
is completely unpressurised, uncovered
(unimmersed) and mounted in its final posi-
tion.
2. Set the function switch to position [A ]. The
display indicates now the actual sensor
current in mA. Save the current status by
pushing the [+/- ] keys simultaneously.
Adjustment in mA without changing the
level
For this adjustment procedure, two sensor
current values (4 ... 20 mA) must be entered
corresponding to the levels 0 % and 100 %.
When using a pressure transmitter, an offset
correction should be carried out to reach maxi-
mum accuracy. Carry out this offset correction
before adjustment and with the sensor unco-
vered (unimmersed).
→
Now select the position [D] or [E] on the
function switch, enter the current values in
mA for min. or max. adjustment and save
your settings.
Adjustment in % by changing the level
During this adjustment procedure, the cur-
26
rent level is assigned to a certain percentage
value. For this reason, percentage values that
correspond to the actual filling levels must be
entered for the min. and max. adjustment. The
ideal calibration is at 0 % and 100 %. Because
it is not always possible to empty or fill a
vessel completely, any value can of course be
entered. The greater the difference between
the two adjustment points, the more precise the
measurement. It does not matter which value is
entered first.
→
Select position [B] or [C] on the function
switch, enter the percentage values for the
min. and max. adjustment and save your
settings.
Relay outputs
Two operating relays are integrated inVE-
GAMET 381 for level detection. First of all,
determine at which switching points the relays
should switch on and off again. Furthermore you
have to distinguish between the relay modes
overfill and dry run protection. You switch over
by exchanging the ON/OFF values of the relay.
•
Overflow protection: Relay is switched
off when the max. level is exceeded (safe
currentless state), relay is switched on again
when the level falls below the min. level
(switch-on point < switch-off point)
•
Dry run protection: Relay is switched off
when the level falls below the min. level (safe
currentless state), relay is switched on again
when the max. level is exceeded (switch-on
point > switch-off point)
→
To adjust the on and off switching points of
relay 1, set the function switch to position
[1] or [2], enter the switching points for ON
or OFF and save your settings. If necessary,
proceed in the same way with relay 2 (posi-
tion [3] or [4]).
VEGAMET 381 • 4 ... 20 mA signal conditioning instrument
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