VTI Instruments EX1000A, User Manual

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EX10xxA Theory of Operation 279
S
ECTION
8
T
HEORY OF
O
PERATION
I
NTRODUCTION
The block diagram in Figure 7-1 illustrates the key components of the analog circuitry. Each of the
main blocks is described below.
R to V
Converter
50-PIN D-SUB CONNECTOR
EX1000A = 3 places
EX1016A = 2 places
EX1032A = 1 place
CH15
INPUT
PROTECTION
LOW PASS FILTER
2287 Hz
DIFFERENTIAL &
COMMON MODE
CALIBRATION
BUS
CH0
Per Channel Circuitry (1 of 48)
INSTRUMENTATION
AMPLIFIER PROGRAMMABLE
LOW PASS FILTER
2-POLE BESSEL @
4, 15, 40, 100, AND 500 Hz
1-POLE BUTTERWORTH
@ 1286 Hz
6
0
:1
M
U
L
T
IP
L
E
X
O
R
16-BIT ADC
±10 V
SYSTEM
REFERENCE
INTERNAL
CALIBRATION
REFERENCES
ISOTHERMAL INTERFACE
EX1016A = 4 places
EX1032A = 8 places
EX1048A = 12 places
EX1000A-TC = 12 places
EXT THERMISTOR
– COLD
JUNCTION COMPENSATION
+
-
+
-
+
- BUFFER
R to V
Converter
THERMISTOR
– COLD
JUNCTION COMPENSATION
+
-
+
-
+
-
+
-
+VBIAS (OTD)
-VBIAS (OTD)
CALIBRATION
SENSE
F
IGURE
7-1: EX10
XX
A A
NALOG
C
IRCUITRY
B
LOCK
D
IAGRAM
V
OLTAGE
/ T
HERMOCOUPLE
I
NPUT
O
PTIONS
Each input channel, dependant on the model, will be either a type “U” (copper) miniature
thermocouple connector or will be part of a 50-pin D-sub connector. See Table 2-3 for pin
assignments of the D-sub connectors.
Thermocouple Connector Inputs
Each group of four thermocouple connectors is tightly coupled to an internal temperature circuit,
providing very accurate cold junction compensation. On either side of the front panel, two nickel
plated banana jacks as available which connect directly to the chassis. These jacks allow the shield
to be connected to chassis using short wires when shielded thermocouples or test wires are used.