Design and theory of operation
20169223D 3-13
DUAL ANALOGUE PCB
The Dual Analogue PCB contains two identical circuits, each
providing a galvanic isolated analogue voltage, ±10V, 0-30V or 4-
20mA current. There is also a 10 kHz oscillator for feedback signal to
enable the ±10V signal from the control unit, jumpered in by S21 and
S22 in pos. 1.
The simplified diagram shows only one of the two circuits, and the
component numbers differs by 10.
The input signal is normally the ±10V from the control unit, selected
by S1 and S2 in pos. 1.
By setting S1 and S2 in pos. 2, an external signal connected to TB21 5 -
6 is selected as input signal.
The signal is then connected to IC2, the AD converter where the
output signal is galvanic isolated from the input signal.
When the 4-20 mA signal is used, the input signal to IC3 must be 0-
10V for ±10V input signal to the AD converter. This is obtained by
setting the SW 1-1 switch in pos. 1, thus connecting the voltage
divider R1/R2. SW1-2 must be placed in pos. 1 (ON) to connect the
DC/DC converter. RV4 is used to adjust the 0V output for -10V input
of IC2.
The DC/DC (IC4) converter, providing ±15V, is used for supply
voltage to the 4-20 mA current generator consisting of IC3, Q1 - Q2
and Q3. The 4-20 mA current is adjusted by RV1 (4mA) and RV2
(20mA). The current return line is connected to the DC/DC converter
neg. output (-15V).
The maximum load resistance for the current output is limited to 500
ohm.
The voltage output may be selected to operate as 0±10V or less,
adjusted by the attenuator RV5. For this output, switches SW1-1 shall
be set to 0 (open) and SW1-3 shall be in pos. 1 (closed). An offset of
±3V may be adjusted by RV3.
The voltage output may also be selected to work from +12 ±6V or
similar when using the DC/DC converter. The switches SW1-3 and 4
shall be in pos. 1 (ON). The output voltage can be adjusted by RV4,
RV3 and RV1 for proper midpoint and max/min voltages.
Minimum load resistance for ±10V signal is 2K, and for 6-12-18
signals (with DC/DC converter) the load is 36K.
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