9
11. DRA-DCC-8 CALIBRATION
Generally there is no need to calibrate the DRA-DCC-8 unit. However if calibration
is required, the following steps should be carried out: Two potentiometer trimmers,
one for "Zero" and the other for "Span" are located on printed card 7040. The
trimmer close to the card edge is the "Zero". Use the following switch setup for
switching all the outputs between 4 and 20mA
Step 1:
Select one channel (for example ch.#1) for the initial tuning. Set the DIPswitch array
to "all 4mA".
Apply supply voltage to the unit. The initial state of all the output currents is 4 mA.
Use SW2 to switch all the outputs between 4 and 20mA. Iteratively set the "Zero"
and the "Span" trimmers for 4.00mA and 20.00mA.
Step 2:
Monitor all the 8 channels in 4mA state, and calibrate the Zero trimmer so that
their average readings is 4.000mA.
Then repeat for 20mA state, and calibrate the Span trimmer so that their average
readings is 20.000mA. This procedure should be repeated until calibration is
satisfactory.
In the parallel control mode, internal pull-up resistors on each of the input terminals
keep them in logical 1 state. The unit will recognize input voltage up to 0.5V as
logical 0 and voltages from 4V to 60V as logical 1.
Note: After every power on, the unit is reset and the initialized
default output currents are according to the SW6 setting
(see para #5.2).
Note: Set the unit to sink mode (fig.2).
S1
S2
S3
S4
S5
S6
S7
ALL CH. = 4mA
ON
OFF
OFF
OFF
X
ALL CH. = 20mA
ON
OFF
ON OFF
X
X
X
X
X
MODE
The channel LEDs are connected in series with the output current so that they will
light only as an indication of a closed current loop.
