Instruction Manual
ExTox Control Units Series ET-8D and ET-4D2
Page 18 of 39
4.5.2
Series ET-4D2
Menu Text
Selection
Function
Selection via F1 (20mA): Analogue Inputs 4..20 mA
CH1 to CH4
0.00 to
25.00 mA
The actual value of the transmitter output current which is
pending at the entry of the control unit prior to processing
is displayed.
Selection via F4 (U
int
): Analogue Inputs U
int
V
cc
4.75 V … 5.25 V: internal power supply (digital)
U
Batt
2.00 V … 4.50 V: battery power of real time clock
+24 V
20.00 V … 27.00 V: power supply control unit
+24 V Rel
20.00 V … 27.00 V: power supply relays
Only type ET4-DA2: For testing purposes (only in menu U
int
and in Access Level 3) constant
values can be issued at the analogue outputs via F6+F2. Starting at Channel 1 with 4 mA,
the output current increases with rising channel number in steps of 1 mA. In consequence
Channel 4 issues 7 mA. The test function can be left via F6+F3.
4.6
Adjustment
This chapter describes the adjustment of transmitters at the control unit.
The Control Units are in general used with transmitters which dispose of a linear 4-20 mA
output that means the current input of 4 mA is interpreted as zero point and the input cur-
rent of 20 mA as end value of measuring range. In between conversion is done linear ac-
cording to the following formula:
range
measuring
of
value
End
mA
16
mA
4
current
Measured
value
Measured
Corrections of settings are done at the transmitter itself and not at the control unit.
In case this is impossible, such as for example due to the fact that the transmitter is hardly
accessible for maintenance purposes, both control units offer the possibility of a device in-
ternal adjustment. To perform this, the measured current value is converted with an offset
and a gain factor after recording of the transmitter signal. After that formation and evalua-
tion of the measured value are done. Necessary settings can be performed in the menu
points OFFSET and GAIN. These corrections correspond to the adjustment of zero point and
sensitivity at the transmitter itself.
Attention: The range of correction values is limited to restrict the adjustment to convenient
tolerance range as far as measuring techniques are concerned. Further corrections have to
be performed directly at the corresponding transmitter, where required the sensor element
has to be exchanged.
The adjustment is done in two steps. During application of zero gas first of all the offset is
changed until the actual value indicated on the display is 4 mA or 0. Then the gain is ad-
justed while applying test gas until the actual value indicated on the display corresponds to
the nominal value.
Attention: In case a measuring point is selected for adjustment, the actual alarm status is
frozen. Alarm and fault messages are neither re-triggered nor deleted, as long as this
measuring point is in adjustment. When changing the measuring point or leaving the ad-
justment menu status is actualised.
