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PDF XTR101 Data sheet ( Hoja de datos )
| Número de pieza | XTR101 | |
| Descripción | Precision/ Low Drift 4-20mA TWO-WIRE TRANSMITTER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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® XTR101
Precision, Low Drift
4-20mA TWO-WIRE TRANSMITTER
FEATURES
q INSTRUMENTATION AMPLIFIER INPUT
Low Offset Voltage, 30µV max
Low Voltage Drift, 0.75µV/°C max
Low Nonlinearity, 0.01% max
q TRUE TWO-WIRE OPERATION
Power and Signal on One Wire Pair
Current Mode Signal Transmission
High Noise Immunity
q DUAL MATCHED CURRENT SOURCES
q WIDE SUPPLY RANGE: 11.6V to 40V
q –40°C to +85°C SPECIFICATION RANGE
q SMALL 14-PIN DIP PACKAGE, CERAMIC
AND PLASTIC
DESCRIPTION
The XTR101 is a microcircuit, 4-20mA, two-wire
transmitter containing a high accuracy instrumenta-
tion amplifier (IA), a voltage-controlled output current
source, and dual-matched precision current reference.
This combination is ideally suited for remote signal
conditioning of a wide variety of transducers such as
thermocouples, RTDs, thermistors, and strain gauge
bridges. State-of-the-art design and laser-trimming,
wide temperature range operation and small size make
it very suitable for industrial process control applica-
tions. In addition, the optional external transistor al-
lows even higher precision.
The two-wire transmitter allows signal and power to
be supplied on a single wire-pair by modulating the
power supply current with the input signal source. The
transmitter is immune to voltage drops from long runs
and noise from motors, relays, actuators, switches,
transformers, and industrial equipment. It can be used
by OEMs producing transmitter modules or by data
acquisition system manufacturers.
APPLICATIONS
q INDUSTRIAL PROCESS CONTROL
Pressure Transmitters
Temperature Transmitters
Millivolt Transmitters
q RESISTANCE BRIDGE INPUTS
q THERMOCOUPLE INPUTS
q RTD INPUTS
q CURRENT SHUNT (mV) INPUTS
q PRECISION DUAL CURRENT SOURCES
q AUTOMATED MANUFACTURING
q POWER/PLANT ENERGY SYSTEM
MONITORING
IREF1
IREF2
Optional
External
e1
3–
10
+VCC Transistor
11
8
5
Span
6
XTR101
(1)
12
B
e2 4 +
9
(1)
13 E
1 2 14 7
Optional
Offset Null
IOUT
NOTE: (1) Pins 12 and 13 are used for optional BW control.
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1986 Burr-Brown Corporation
PDS-627G
Printed in U.S.A. October, 1993
1 page  
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, +VCC = 24VDC, unless otherwise noted.
INPUT VOLTAGE NOISE DENSITY vs FREQUENCY
60
50
40
30
20
10
0
1
10 100 1k 10k 100k
Frequency (Hz)
INPUT CURRENT NOISE DENSITY vs FREQUENCY
6
5
4
3
2
1
0
1 10 100 1k 10k 100k
Frequency (Hz)
OUTPUT CURRENT NOISE DENSITY vs FREQUENCY
6
5
4
3
2
1
0
1 10 100 1k 10k 100k
Frequency (Hz)
THEORY OF OPERATION
A simplified schematic of the XTR101 is shown in Figure 1.
Basically the amplifiers, A1 and A2, act as a single power
supply instrumentation amplifier controlling a current source,
A3 and Q1. Operation is determined by an internal feedback
loop. e1 applied to pin 3 will also appear at pin 5 and
similarly e2 will appear at pin 6. Therefore the current in RS,
the span setting resistor, will be IS = (e2 – e1)/RS = eIN/RS.
This current combines with the current, I3, to form I1. The
circuit is configured such that I2 is 19 times I1. From this
point the derivation of the transfer function is straightfor-
since IO is unipolar e2 must be kept larger than e1; i.e., e2 ≥
e1 or eIN ≥ 0. Also note that in order not to exceed the output
upper range limit of 20mA, eIN must be kept less than 1V
when RS = ∞ and proportionately less as RS is reduced.
INSTALLATION AND
OPERATING INSTRUCTIONS
BASIC CONNECTION
ward but lengthy. The result is shown in Figure 1.
The basic connection of the XTR101 is shown in Figure 1.
Examination of the transfer function shows that IO has a
lower range-limit of 4mA when eIN = e2 – e1 = 0V. This 4mA
is composed of 2mA quiescent current exiting pin 7 plus
2mA from the current sources. The upper range limit of IO is
set to 20mA by the proper selection of RS based on the upper
range limit of eIN. Specifically RS is chosen for a 16mA
output current span for the given full scale input voltage
span; i.e., (0.016 + 40/RS)(eIN full scale) = 16mA. Note that
A difference voltage applied between input pins 3 and 4 will
cause a current of 4-20mA to circulate in the two-wire
output loop (through RL, VPS, and D1). For applications
requiring moderate accuracy, the XTR101 operates very
cost-effectively with just its internal drive transistor. For
more demanding applications (high accuracy in high gain)
an external NPN transistor can be added in parallel with the
internal one. This keeps the heat out of the XTR101 package
®
5 XTR101
5 Page 
1mA
+
VD D
–
+
R5 V5
–
+
R6 V6
–
FIGURE 11. Cold Junction Compensation Circuit.
the thermocouple impedance goes very high. The circuits of
Figures 16 and 17 inherently have down scale indication.
When the impedance of the thermocouple gets very large
(open) the bias current flowing into the + input (large
impedance) will cause IO to go to its lower range limit value
(about 3.8mA). If up scale indication is desired the circuit of
Figure 18 should be used. When the TC opens the output will
go to its upper range limit value (about 25mA or higher).
OPTIONAL INPUT OFFSET VOLTAGE TRIM
The XTR101 has provisions for nulling the input offset
voltage associated with the input amplifiers. In many appli-
cations the already low offset voltages (30µV max for the B
grade, 60µV max for the A grade) will not need to be nulled
at all. The null adjustment can be done with a potentiometer
at pins 1, 2 and 14 as shown in Figures 5 and 6. Either of
these two circuits may be used. NOTE: It is not recom-
mended to use this input offset voltage nulling capability for
elevation or suppression. See the Signal Suppression and
Elevation section for the proper techniques.
OPTIONAL BANDWIDTH CONTROL
Low-pass filtering is recommended where possible and can
be done by either one of two techniques shown in Figure 12.
C2 connected to pins 3 and 4 will reduce the bandwidth with
a cutoff frequency given by,
15.9
fCO = (R1 + R2 + R3 + R4) (C2 + 3pF)
This method has the disadvantage of having fCO vary with
R1, R2, R3, R4, and it may require large values of R3 and R4.
The other method, using C1, will use smaller values of
capacitance and is not a function of the input resistors. It is,
however, more subject to nonlinear distortion caused by
slew rate limiting. This is normally not a problem with the
slow signals associated with most process control transduc-
ers. The relationship between C1 and fCO is shown in the
Typical Performance Curves.
1mA
R3(1)
3 11
–
1mA
C2 XTR101
R1
R4(1)
4+
13
R2 12 C1
0.0047µF
NOTE: (1) R3 and R4 should be equal if used.
Internally eNOISE RTI = e2INPUT STAGE + e2OUTPUT STAGE 2
Gain
FIGURE 12. Optional Filtering.
APPLICATION CIRCUITS
XTR101
Voltage
Reference
+
MC1403A
VR = 2.5V
–
100pF
IO
(4-20mA)
V+
OPA27
R1
125Ω
V–
R2
500Ω
IO(1) (0-20mA)
NOTE: (1) IO =
1+
R1
R2
IO –
VR
R2
= 1.25 IO – 5mA
Other conversions are readily achievable by
changing the reference and ratio of R1 to R2.
FIGURE 13. 0-20mA Output Converter.
®
11 XTR101
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet XTR101.PDF ] | |
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