Parker ACR9000, Руководство по установке

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Parker Hannifin
Transmission Cycle Period
ACR90x0 uses a periodic cyclic transmission protocol between the master
and the nodes for digital and analog outputs, and for analog inputs. Digital
inputs transmit to the ACR90x0 only when their input state has changed.
Each cycle, the master sends a synchronization message to all slave nodes.
The slave nodes respond by latching and transmitting back their analog
inputs, and by asserting the output states commanded by the master before
the synchronization message. The cycle period should be calculated to be as
fast as possible, and is dependent on the bit rate, the node types, and the
number I/O bits on the nodes. Two factors limit the speed of the transmission
cycle. One is the total amount data that needs to be transmitted at the
selected bit rate. The other is the processing load of the slowest node on the
bus.
For the former constraint, the number of bits is divided by the bit rate for the
required time. Bits are sent in messages of 125 bits each. Each node has
messages for its data, plus one to report health. The ACR90x0 also sends a
sync message. In the formulas below, digital inputs are ignored, since these
will not transmit periodically.
Node messages = (node analog 3)/4 + (node digital outputs
+63)/64 + (node analog o3)/4 + 1
Total messages = Sum of Node me1
Required time (milliseconds) = (Total messages * 125) /bit rate in
Kilobits/s
This time should be rounded up to the next higher integer number of
milliseconds. For example, suppose there are two nodes. One node has 100
digital outputs and 10 each analog inputs and outputs. The second node has
20 digital outputs and 5 each analog inputs and outputs. The first node has
nine messages, and the second has six messages. The total is 16
messages. At the 1-megabit rate, 2 milliseconds are required. At the 125K
rate, 16 milliseconds are required.
(16 * 125)/1000 = 2
(16 * 125)/125 = 16
The second constraint is individual node speed. Parker offers the PIO-337
and PIO-347 fieldbus couplers, and these have been characterized for
speed. The time required depends on the coupler and the amount and type
of I/O on the coupler. There is a base time required just to respond to the
ACR90x0’s sync signal, plus additional time per point. The sum represents
minimum type required by the node. Using the first node of the example
above, and the timing in the table below, the time using a PIO-347 would be
31 milliseconds, and using a PIO-337 would be five milliseconds. Using the
second node of the example above, and the timing in the table below, the
time using a PIO-347 would be 12 milliseconds, and using a PIO-337 would
be two milliseconds.
Node
Type Base time
(milliseconds) time/digital point
(microseconds) time/analog point
(microseconds)
PIO-347 5 100 270
PIO-337 1 15 40
130 ACR9000 Series Hardware Installation Guide
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