Impulse DSCT34 - Manual

DIN Rail Mount Two-WireTransmitters DSCT
For information call 800-444-7644 204
DSCT34
Linearized 2- or 3-Wire RTD Input Transmitters
Figure 1: DSCT34 Block Diagram
▲
Features
• Interfaces to 100 Ω Platinum or 120 Ω
Nickel RTDs
• Linearizes RTD Signal
• Process Current Output
• 1500Vrms Transformer Isolation
• ANSI/IEEE C37.90.1 Transient Protection
• Input and Output Protected to 240VAC Continuous
• Up to 60V Loop Voltage
• 160dB CMR
• 85dB NMR at 60Hz, 80dB at 50Hz
• ±0.1% Accuracy
• ±0.025% Conformity
• Easily Mounts on Standard DIN Rail
• CSA and FM Approvals Pending
• CE Compliant
Description
Each DSCT34 RTD input transmitter provides a single channel of RTD input
which is filtered, isolated, amplified, linearized, and converted to a process
current output (Figure 1). Signal filtering is accomplished with a five-pole filter,
which provides 85dB of normal-mode-rejection at 60Hz and 80dB at 50Hz. An
anti-aliasing pole is located on the field side of the isolation barrier, and the other
four are on the process loop side. After the initial field-side filtering, the input signal
is chopped by a proprietary chopper circuit. Isolation is provided by transformer
coupling, again using a proprietary technique to suppress transmission of
common mode spikes or surges.
RTD excitation is provided from the transmitter using a precision current source.
The excitation currents are very small (0.26mA max for 100 Ω Pt and 120 Ω Ni)
which minimizes self-heating of the RTD. Linearization is achieved by creating
a non-linear transfer function through the module itself. This non-linear transfer
function is configured at the factory and is designed to be equal and opposite
to the specific RTD non-linearity. Lead compensation is achieved by matching
two current paths thus canceling the effects of lead resistance.
The specifications listed are for a 3-wire connection. A 2-wire connection of the
RTD to the module is also possible and is achieved by adding a jumper between
pin 5 (+EXC) and pin 6 (+IN) on the terminal block and connecting the RTD leads
between pin 6 (+IN) and pin 7 (-IN). The 2-wire connection nullifies the lead
resistance compensation feature of the module.
Special input and output circuits on the DSCT34 transmitters provide protection
against accidental connection of power-line voltages up to 240VAC and against
transient events as defined by ANSI/IEEE C37.90.1. Signal and loop 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 ±3% 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.