Each DSCA45 frequency input module provides a single channel of frequency input which is isolated and converted to a standard analog voltage or current output.
The frequency input signal can be a TTL level or zero-crossing signal. Terminal 7 (-IN) on the field-side terminal block is the “common” or ground connection for input signals. A TTL signal is connected from terminal 6 (+IN) to terminal 7 (-IN), while a zero-crossing signal is connected from terminal 5 (+EXC) to terminal 7 (-IN). Input circuitry for each of the signal types has hysteresis built in. An input signal must cross entirely through the hysteresis region in order to trigger the threshold comparator.
A +5.1V excitation is available for use with magnetic pick-up or contact-closure type sensors. The excitation is available on terminal 8 (-EXC) with return at terminal 7 (-IN).
Module output is either voltage or current. For current output models a dedicated loop supply is provided at terminal 3 (+OUT) with loop return located at terminal 4 (-OUT). The system-side load may be either floating or grounded.
Special input circuits provide protection against accidental connection of power-line voltages up to 240VAC and against transient events as defined by ANSI/IEEE C37.90.1. Protection circuits are also present on the signal output and power input terminals to guard against transient events and power reversal. Signal and power lines are secured to the module using screw terminals which are in pluggable terminal blocks for ease of system assembly and reconfiguration.
The modules have excellent stability over time and do not require recalibration, however, zero and span settings are adjustable up to ±5% to accommodate situations where fine-tuning is desired. The adjustments are made using potentiometers located under the front panel label and are non-interactive for ease of use.