GE VMIVME-5530S Gas turbine control card

Cable Length and Frequency When cable length or frequency goes up, your selection of cable becomes even more critical. Long cables can result in changes in duty cycle, rise and fall times, and phase relationships. The phase relationship between channels A and B in encoder X1 and X4 mode is critical. The maximum encoder input of 250KHz is designed to work with Allen-Bradley Bulletin 845H or similar incremental encoders with a quadrature specification of 90o (+22o) and a duty cycle specification of 50% (+10%). Any additional phase or duty cycle changes caused by the cable will reduce the specified 250KHz specification. For any application over 100 feet, and/or over 100KHz, use Belden 9182, a high performance twisted-pair cable with 100% foil shield, a drain wire, moderate 150 ohm inpedance and low capacitance per unit length.

Cable Capacitance 

Use cable with a low capacitance as measured per unit length. High capacitance rounds off incoming square wave edges and takes driver current to charge and discharge. Increasing cable length causes a linear increase in capacitance, which reduces the maximum usable frequency. This is especially true for open collector drivers with resistive pull-ups. For example, Belden 9182 is rated at a very low 9pF/foot.

Questions and Answers 

This appendix presents some of the more commonly asked questions about application and operation of the Very High Speed Counter module. The following questions and answers do not cover all possible questions, but are representative of the more common ones. Q. If I do not connect channel B in counter mode, what happens to the count status? A. With channel B disconnected or tied low, the module will count up only. If channel B is tied high, it will count down.

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