Renishaw RCU10, Инструкция по установке и эксплуатации

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Connector pinout and hardware installation details B-9
B.4.2 Wiring requirements
A cable with twisted pairs and overall shield is recommended for the digital quadrature
interface between the RCU10 and the encoder, as specified in EIA RS 422 (e.g. Belden
8107).
Maximum cable length is dependent on the update rate of the quadrature signals;
recommendations are shown in the graph below. For encoders where the quadrature
state transition is asynchronous in nature, the update rate applies to a minimum transition
(minimum edge to edge separation between the quadrature signals)
The quadrature, reference and error lines are all terminated inside the RCU unit:
• The quadrature line differential pair is dc terminated with a 120 Ω resistor.
• The reference line differential pair is ac terminated with a series connected 120 Ω
resistor and 1 nF capacitor.
•
The error line differential pair is ac terminated with a series 1
20 Ω resistor and 10 nF
capacitor. In addition, the line is pulled active in the event of a disconnection to either
signal.
All the encoder port terminals are protected from wiring faults that would be expected
when used with HS10, RLE10 and linear encoders powered from 5 V. Where a short
circuit could flow, PCB tracks are rated to 0.5 A.
A method is employed to sense disconnection of one or more of the quadrature lines in
addition to the standard EIA–RS422 line receivers. A circuit monitors the difference
voltage across each quadrature pair and reports a fault if the level falls below a given
voltage threshold (< +0.75 V or > -0.75 V).
NOTE: To ensure that a false disconnection alarm does not occur during normal
operation, it is important that the encoder complies with the minimum drive level of 2 V
and is within the maximum cable length for the signal bandwidth.
RS422 Cable Length vs Update Rate
1.00
10.00
100.00
1000.00
1.00 10.00 100.00
Update rate Mhz
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