Rockwell Automation 1395 Digital Reference Adapter Board - Manual (Page 55)

Chapter 6
StartĆUp
6-9
Analog Outputs – Analog Outputs are similar to analog inputs with the
exception that there are no programmable analog gain and offset
parameters. Each output has a digital scale and digital offset parameter,
along with a specific fast parameter used for linking. Differences occur
because of the direction of information flow. The Drive sends a digital
value in Drive units which must be converted to an analog signal for use by
an external device. As with the analog inputs, the analog outputs convert a
+/– 2048 digital value to a +/– 10V DC analog value. Thus, when the Drive
sends +/– 100% base speed (equal to +/– 4096) to an analog output it must
be scaled by 0.5 to be in the proper range.
Analog Output 1 and Analog Output 2 will be used as examples in
detailing the scaling and offset parameters. At Analog Output 1, a meter
with a range of 0 to 10 VDC has been connected. Parameter 451 has been
linked to Parameter 106, Velocity Feedback. In order for the meter to
indicate speed in both directions, the scale and offset parameters must be
adjusted (see
Figure 6.5 ). Working in the opposite direction as the analog
inputs, apply the scaling factor first. The Drive will send a
±
4096 signal
value to indicate
±
100% velocity feedback, for a total digital range of
8192. The meter, having an analog range of 0 to 10 VDC, requires a digital
range of 2048. By applying a scale factor of 0.25 this is accomplished
(8192 x 0.25 = 2048). In order to have the 0 to 10 VDC meter indicate
±
100% feedback, an offset must be applied. Offset parameters for analog
outputs will again add the corresponding digital value to the range. In this
case, an offset of 5 volts adds a digital value of 1024 to the range. This will
allow full range deflection on the 0 to 10 volt meter, with 5 volts indicating
zero speed.