3-17
To measure the PC bus clock frequency, DriverLINX requires that
Counters 1 and 2 be chained together using an external jumper. To chain
the counters, connect Counter 2 Out [6] to Counter 1 IN [4] on the DAS-8
external connector.
Then, using DriverLINX, select the Counter/Timer Section in the
Configuration Dialog Box. Choosing Custom Clock in the drop-down list
of the Resolution combo-box displays the Custom Clock Frequency
Dialog Box. Selecting Measure will start a 30-second measuring interval
for determination of the PC bus clock frequency. The frequency box will
update every second with the currently measured frequency. The
measuring interval may be stopped at any time using the Stop pushbutton.
The displayed frequency is added to the Resolution list box by selecting
OK, or the measurement can be abandoned by selecting Cancel. The
displayed frequency may be edited manually by selecting the numbers in
the edit box and typing a new value for the selected digits.
4–20mA Current Loops
Process control current-loop transducers interface easily with DAS-8 and
DAS-8/LT by adding a suitable shunt resistor across the input. Since the
maximum current is 20mA and the maximum input range of a DAS-8 is
+5V, a 250-ohm precision shunt resistor is required. The
DAS-8/PGA(G2) and DAS-8/AO default range is also ±5V, so that this
method also works here. The resistor should be of low temperature-
coefficient metal film or wirewound construction for stability with time
and temperature.
Using this interface, the 4–20mA working range of the current loop
corresponds to 1638 bits of input, a resolution of about 0.06%.
The Reference (DAS-8 and DAS-8/LT Only)
The DAS-8 and DAS-8/LT provide a +10V A/D voltage reference (Vref).
It may be used for offsetting signals, but should not be heavily loaded.
The maximum available output current is 2mA. Since this reference is
shared by the A/D, any overload or shorting of the reference will affect
the scaling of the A/D.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com