SCM5B37
Thermocouple Input Modules
FEATURES
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INTERFACES TO TYPES J, K, T, E, R, S, C, N AND B
THERMOCOUPLES
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HIGH LEVEL VOLTAGE OUTPUTS
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1500Vrms TRANSFORMER ISOLATION
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ANSI/IEEE C37.90.1-1989 TRANSIENT PROTECTION
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INPUT PROTECTED TO 240VAC CONTINUOUS
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160dB CMR
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95dB NMR AT 60Hz, 90dB at 50Hz
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鹵0.05%
ACCURACY
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鹵0.02%
LINEARITY
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鹵1碌V/擄C
DRIFT
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CSA CERTIFIED, FM APPROVED, CE COMPLIANT
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MIX AND MATCH SCM5B TYPES ON BACKPANEL
The SCM5B modules are designed with a completely isolated computer
side circuit which can be floated to
鹵50V
from Power Common, pin 16. This
complete isolation means that no connection is required between I/O
Common and Power Common for proper operation of the output switch. If
desired, the output switch can be turned on continuously by simply
connecting pin 22, the Read-Enable pin to I/O Common, pin 19.
The SCM5B37 can interface to nine industry standard thermocouple types:
J, K, T, E, R, S, C, N, and B. Its corresponding output signal operates over
a 0V to +5V range. Each module is cold-junction compensated to correct
for parasitic thermocouples formed by the thermocouple wire and screw
terminals on the mounting backpanel. Upscale open thermocouple detect
is provided by an internal pull-up resistor. Downscale indication can be
implemented by installing an external 47M鈩?resistor,
鹵20%
tolerance,
between screw terminals 1 and 3 on the SCMPB01/02/03/04/05/06
backpanels.
Signal filtering is accomplished with a six-pole filter which provides 95dB
of normal-mode-rejection at 60Hz and 90dB at 50Hz. Two poles of this filter
are on the field side of the isolation barrier, and the other four are on the
computer 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. The module is powered from +5VDC,
鹵5%.
A special input circuit on the SCM5B37 modules provides protection
against accidental connection of power-line voltages up to 240VAC.
For Class I, Division 2 hazardous location applications, refer to Dataforth
installation manual MA1146 (available upon request).
DESCRIPTION
Each SCM5B37 thermocouple input module provides a single channel of
thermocouple input which is filtered, isolated, amplified, and converted to
a high level analog voltage output (Figure 1). This voltage output is logic-
switch controlled, allowing these modules to share a common analog bus
without the requirement of external multiplexers.
+2.5V
100M鈩?/div>
4
NC
4
+In
Thermocouple
鈥揑n
鈥揈XC
1
3
5
2
3
6
Surge
Suppression
and
Protection
+EXC
LPF
Isochopper鈩?/div>
Amplifier
Pat Pending
LPF
20
V
OUT
19
+V
鈥揤
22
I/O Common
Precision
Reference
Isolated
Computer-Side
Power
RD EN\
Backpanel
Term Block
1
2
Temp
Sensor
CJC
+V
鈥揤
17
Isolated
Field-Side
Power
Power
Oscillator
+5V
16
Power Common
FIGURE 1. SCM5B37 Block Diagram.
DATAFORTH
A Burr-Brown Company
廬
Call 800-444-7644
For Information and Assistance
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