DSCA33 Isolated True RMS Input Signal Conditioners

Description 

Each DSCA33 True RMS input module provides a single channel of AC  input which is converted to its True R0S D& value, filtered, isolated,  amplified, and converted to standard process voltage or current output  (Figure 1). 

The field voltage or current input signal is processed through an A&  coupled preamplifier and R0S converter on the field side of the  isolation barrier. The converted dc signal is then filtered and chopped by a  proprietary chopper circuit and transferred across the transformer  isolation barrier, suppressing transmission of common mode spiNes and  surges. The computer side circuitry reconstructs, filters and converts the  signal to industry standard outputs. 

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  O8T. The systemside load may be either Àoating  or grounded. Special input circuits provide protection against accidental connection of  powerline voltages up to 9A& and against transient events as defined  by ANSII((( &... 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 pluggable terminal blocNs for ease of system  assembly and reconfiguration. 

DS&A-33 modules have excellent stability over time and do not reTuire  recalibration, however, both ]ero and span settings are adMustable to  accommodate situations where fine tuning is desired. The adMustments  are made using potentiometers located under the front panel label and  are non-interactive for ease of use. 

Due to circuit limitations, DSCA33-04x and -05x are not ATEX compliant.

Features 

• Interfaces RMS Voltage (0 – 300V) or  RMS Current (0 – 5A) 

• Designed for Standard Operation with  Frequencies of 45Hz to 1000Hz  (Extended Range Operation to 20kHz) ‡ &ompatible with Standard &urrent and Potential  Transformers 

• Industry Standard Output of 0 to 1mA,  0 to 20mA, 4 to 20mA, 0 to +5V, or 0 to +10V ‡ “. Factory &alibrated Accuracy  (Accuracy Class 0.2) ‡ “ AdMustable =ero and Span 

• 1500Vrms Transformer Isolation 

• Input Overload Protected to 480V  (Peak AC & DC) or 10Arms Continuous 

• 100dB CMR • ANSI/IEEE C37.90.1 Transient Protection 

• Easily Mounts on Standard DIN Rail 

• C-UL-US Listed and CE Compliant 

• ATEX Compliant (all models except  DSCA33-04x, -05x)

of the sensing transformer. Using the sensing transformer ratio of 35:1, the  AFT and ALT Values on the 4160 Volt side of the sensing transformer is  equal to +/- 0.30 Volts x 35. The Loss of Voltage AFT and ALT Values are  +/- 10.5 Volts about the NTS of 2975 Volts.  

 The winding ratio of the sensing potential transformer is 35:1.  

 The Analytical Limit (AL) for Degraded Voltage is 3683V and for LOP is  2912V. The ALs have not changed in the calculation.  

 There are not any physical bistable relays. They are modeled in software.  The pickup and dropout voltages are the ‘Setpoint’ and ‘Reset’ values. The  values and tolerances on the 120 Volt side of the sensing transformer for  degraded voltage and loss of voltage are listed below. A harmonic filter is not  needed because there aren’t any physical relay contacts opening and closing  and generating harmonics when doing so. There is an analog low pass  prefilter and a digital low pass filter built into the analog-to-digital module  (ABB AI620).  Degraded Voltage:  Setpoint (pickup) = 107.03V Hi Limit = 107.33V Low Limit = 106.73V  Reset (dropout) = 108.53V Hi Limit = 108.83V Low Limit = 108.23V  Loss of Voltage:  Setpoint (pickup) = 85.00V Hi Limit = 85.30V Low Limit = 84.70V  Reset (dropout) = 86.50V Hi Limit = 86.80V Low Limit = 86.20V  

 The Dataforth voltage-to-current module part number supplied by  Westinghouse is DSCA33-1566. The accuracy data for this Westinghouse  part number is the same as the non-proprietary accuracy data for Dataforth  part number DSCA33-04C. The non-proprietary data sheet for Dataforth part  number DCCA33-04C is provided as Attachment 1 to this Enclosure. The  ABB analog-to-digital module part number is Al620. The non-proprietary data  sheet for the ABB part number AI620 is provided as Attachment 2 to this  Enclosure.