Section 8; Theory Of Operation; Introduction; Voltage / Thermocouple Input Options - VTI Instruments EX1000A User Manual

T O
HEORY OF
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.
50-PIN D-SUB CONNECTOR
EX1000A = 3 places
EX1016A = 2 places
EX1032A = 1 place
+
CH0
-
+
CH15
-
R to V
+
Converter
-
EXT THERMISTOR – COLD
JUNCTION COMPENSATION
ISOTHERMAL INTERFACE
EX1016A = 4 places
EX1032A = 8 places
EX1048A = 12 places
EX1000A-TC = 12 places
+
-
+
-
R to V
Converter
+
-
THERMISTOR – COLD
JUNCTION COMPENSATION
+
-
F
V / T
OLTAGE HERMOCOUPLE
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.
EX10xxA Theory of Operation
PERATION
Per Channel Circuitry (1 of 48)
LOW PASS FILTER
INPUT
PROTECTION
CALIBRATION
BUS
7-1: EX10 A A
IGURE XX NALOG
I O
NPUT PTIONS
S
ECTION
+VBIAS (OTD)
INSTRUMENTATION
AMPLIFIER
PROGRAMMABLE
LOW PASS FILTER
2287 Hz
2-POLE BESSEL @
DIFFERENTIAL &
4, 15, 40, 100, AND 500 Hz
COMMON MODE
1-POLE BUTTERWORTH
@ 1286 Hz
-VBIAS (OTD)
C B
IRCUITRY LOCK
www.vtiinstruments.com
BUFFER
D
IAGRAM
8
16-BIT ADC
±10 V
SYSTEM
REFERENCE
INTERNAL
CALIBRATION
REFERENCES
CALIBRATION
SENSE
279