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PDF RCV420 Data sheet ( Hoja de datos )
| Número de pieza | RCV420 | |
| Descripción | Precision 4mA to 20mA CURRENT LOOP RECEIVER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RCV420 (archivo pdf) en la parte inferior de esta página. Total 10 Páginas | ||
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®
RCV420
RCV420
Precision 4mA to 20mA
CURRENT LOOP RECEIVER
FEATURES
q COMPLETE 4-20mA TO 0-5V CONVERSION
q INTERNAL SENSE RESISTORS
q PRECISION 10V REFERENCE
q BUILT-IN LEVEL-SHIFTING
q ±40V COMMON-MODE INPUT RANGE
q 0.1% OVERALL CONVERSION ACCURACY
q HIGH NOISE IMMUNITY: 86dB CMR
DESCRIPTION
The RCV420 is a precision current-loop receiver de-
signed to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a pre-
mium grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
The circuit introduces only a 1.5V drop at full scale,
which is useful in loops containing extra instrument
burdens or in intrinsically safe applications where
APPLICATIONS
q PROCESS CONTROL
q INDUSTRIAL CONTROL
q FACTORY AUTOMATION
q DATA ACQUISITION
q SCADA
q RTUs
q ESD
q MACHINE MONITORING
transmitter compliance voltage is at a premium. The
10V reference provides a precise 10V output with a
typical drift of 5ppm/°C.
The RCV420 is completely self-contained and offers a
highly versatile function. No adjustments are needed
for gain, offset, or CMR. This provides three important
advantages over discrete, board-level designs: 1) lower
initial design cost, 2) lower manufacturing cost, and
3) easy, cost-effective field repair of a precision circuit.
RCV420
V+
16
–In 1
300kΩ
RS
75Ω
CT 2
RS
75Ω
+In 3
300kΩ
V– Ref In
4 12
99kΩ
92kΩ
11.5kΩ
1.01kΩ
+10V
Ref
100kΩ
13
Rcv
Com
5
Ref
Com
15 Rcv fB
14 Rcv Out
11 Ref Out
10 Ref fB
8 Ref Trim
7 Ref Noise Reduction
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
©1988 Burr-Brown Corporation
PDS-1837E
RCV420Printed in U.S.A. October, 1997
®
1 page  
THEORY OF OPERATION
Refer to the figure on the first page. For 0 to 5V output with
4–20mA input, the required transimpedance of the circuit is:
VOUT/IIN = 5V/16mA = 0.3125V/mA.
To achieve the desired output (0V for 4mA and 5V for
20mA), the output of the amplifier must be offset by an
amount:
VOS = –(4mA)(0.3125V/mA) = –1.25V.
The input current signal is connected to either +In or –In,
depending on the polarity of the signal, and returned to
ground through the center tap, CT. The balanced input—two
matched 75Ω sense resistors, RS—provides maximum rejec-
tion of common-mode voltage signals on CT and true differ-
ential current-to-voltage conversion. The sense resistors
convert the input current signal into a proportional voltage,
which is amplified by the differential amplifier. The voltage
gain of the amplifier is:
AD = 5V/(16mA)(75Ω) = 4.1667V/V.
The tee network in the feedback path of the amplifier
provides a summing junction used to generate the required
–1.25V offset voltage. The input resistor network provides
high-input impedance and attenuates common-mode input
voltages to levels suitable for the operational amplifier’s
common-mode signal capabilities.
BASIC POWER SUPPLY
AND SIGNAL CONNECTIONS
Figure 1 shows the proper connections for power supply and
signal. Both supplies should be decoupled with 1µF tanta-
lum capacitors as close to the amplifier as possible. To avoid
gain and CMR errors introduced by the external circuit,
connect grounds as indicated, being sure to minimize ground
resistance. The input signal should be connected to either
+In or –In, depending on its polarity, and returned to ground
through the center tap, CT. The output of the voltage refer-
ence, Ref Out, should be connected to Ref In for the
necessary level shifting. If the Ref In pin is not used for level
shifting, then it must be grounded to maintain high CMR.
GAIN AND OFFSET ADJUSTMENT
Figure 2 shows the circuit for adjusting the RCV420 gain.
Increasing the gain of the RCV420 is accomplished by
inserting a small resistor in the feedback path of the ampli-
fier. Increasing the gain using this technique results in CMR
degradation, and therefore, gain adjustments should be kept
as small as possible. For example, a 1% increase in gain is
typically realized with a 125Ω resistor, which degrades
CMR by about 6dB.
A decrease in gain can be achieved by placing matched
resistors in parallel with the sense resistors, also shown in
Figure 2. The adjusted gain is given by the following
expression
VOUT/IIN = 0.3125 x RX /(RX + RS).
A 1% decrease in gain can be achieved with a 7.5kΩ
resistor. It is important to match the parallel resistance on
each sense resistor to maintain high CMR. The TCR mis-
match between the two external resistors will effect gain
error drift and CMR drift.
There are two methods for nulling the RCV420 output offset
voltage. The first method applies to applications using the
internal 10V reference for level shifting. For these applica-
–In 1
10kΩ(1)
CT
RX
2
+In 10kΩ(1) RX 3
15
RCV420
R1 ±0.5% Gain
200Ω(1)
Adjustment
14
Rcv Out
NOTE: (1) Typical values. See text.
FIGURE 2. Optional Gain Adjustment.
IIN +In 3
4–20mA CT 2
–In 1
RS 75Ω
RS 75Ω
RCV420
V+ 16 4 V–
1µF 1µF
12 Ref In
15 Rcv fB
+10V
Reference
14 Rcv Out
11 Ref Out
10 Ref fB
8 Ref Trim
7 Ref Noise Reduction
13 5
Rcv Com Ref Com
VO
(0–5V)
FIGURE 1. Basic Power Supply and Signal Connections.
5
RCV420
®
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet RCV420.PDF ] | |
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