How Do I Use the Index Channel on My [c]FP-QUAD-510?Hardware: FieldPoint>>Discrete I/O Modules>>FP-QUAD-510
Problem: I have an encoder that outputs a pulse each time it completes a revolution. How can I connect this signal to my [c]FP-QUAD-510 properly? Solution: There is a wide variety of motion encoders out on the market for a variety of applications. The [c]FP-QUAD-510 has been designed to accommodate most (if not all) of these encoders. The index value (typically abbreviated ‘I’ or ‘Z’) pulses when an encoder makes a complete revolution and crosses the zero (or initial) position. To properly read this signal in your FieldPoint application, the A and B phase outputs of the encoder must be logic low and the I output logic high. See the figure below:
This condition will latch the index value high (‘1’) on the index channel of the corresponding axis of the [c]FP-QUAD-510. Note that no edges have to occur on any of the channels to latch the value. Once the index channel has been read by software, it will be reset to ‘0.’ A software-read includes an FP Read.vi in LabVIEW as well as monitoring the channel in Measurement and Automation Explorer (MAX). Thus, it is difficult to observe the behavior of the index channels in MAX, because they are reset to ‘0’ almost instantaneously. If the index output of the encoder remains high, the index channel will still be set to ‘0’ after a software-read, but will reset to ‘1’ upon the next read. It will continue to toggle in this manner until the index output goes low. The [c]FP-QUAD-510 module is capable of reading both differential and single-ended encoder outputs. Thus, the module determines “high” and “low” by comparing the relative voltage potentials on A+ & A-, B+ & B-, and I+ and I-. For example, if the signal on A+ is at a higher voltage than that on A-, the module will read a high for Phase A. If, however, the voltage on A- is higher that the voltage on A+, the module will read a low. Many encoders may not have differential phase outputs. In this case, DO NOT simply ground the A-, B-, and I-. Leaving these inputs open will ensure proper operation. The flexibility of field-wiring the [c]FP-QUAD-510 affords you many combinations for interfacing with a variety of encoders. For example, some encoders may not appear to produce the correct timing required to latch the index channel. Observe the figure below:
In such a case, note that you may connect A-NOT to A+, B-NOT to B+, and Z to I +. This will satisfy the conditions to latch a ‘1’ into the index channel with the Z signal pulses. There are several attributes you may associate with the index channel once you have wired it correctly. Refer to the related links below for more information. Related Links: FP-QUAD-510 and cFP-QUAD-510 Operating Instructions KnowledgeBase 3E0DE033: My FP-QUAD-510 Will Not Count KnowledgeBase 3F09A5FJ: External Power Supply Requirements for the [c]FP-QUAD-510 KnowledgeBase 2TQ9JOP6: Using the FP-QUAD-510 with One Phase (Channel) Connected Attachments: 
Report Date: 05/02/2005 Last Updated: 09/19/2005 Document ID: 3L1D9QS9 |
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