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XTR104

型号：

XTR104

描述：

4-20mA电流发送器与电桥激励和线性化[ 4-20mA Current Transmitter with BRIDGE EXCITATION AND LINEARIZATION ]

品牌：

BB[ BURR-BROWN CORPORATION ]

页数：

11 页

PDF大小：

167 K

下载PDF手册
®
XTR104  
4-20mA Current Transmitter with  
BRIDGE EXCITATION AND LINEARIZATION  
FEATURES  
APPLICATIONS  
● LESS THAN ±1% TOTAL ADJUSTED  
● INDUSTRIAL PROCESS CONTROL  
● FACTORY AUTOMATION  
● SCADA  
ERROR, –40°C TO +85°C  
● BRIDGE EXCITATION AND LINEARIZATION  
● WIDE SUPPLY RANGE: 9V to 40V  
● LOW SPAN DRIFT: 50ppm/°C max  
● HIGH PSR: 110dB min  
● WEIGHTING SYSTEMS  
● ACCELEROMETERS  
● HIGH CMR: 80dB min  
BRIDGE NONLINEARITY CORRECTION  
USING XTR104  
2.0  
Uncorrected  
Bridge Output  
DESCRIPTION  
1.5  
1.0  
0.5  
The XTR104 is a monolithic 4-20mA, two-wire cur-  
rent transmitter integrated circuit designed for bridge  
input signals. It provides complete bridge excitation,  
instrumentation amplifier, linearization, and current  
output circuitry necessary for high impedance strain  
gage sensors.  
Corrected  
0
The instrumentation amplifier can be used over a wide  
range of gain, accommodating a variety of input signals  
and sensors. Total adjusted error of the complete current  
transmitter, including the linearized bridge is less than  
±1% over the full –40°C to +85°C temperature range.  
This includes zero drift, span drift and non-linearity for  
bridge outputs as low as 10mV. The XTR104 operates  
on loop power supply voltages down to 9V.  
–0.5  
0mV  
5mV  
Bridge Output  
10mV  
RLIN  
9V to 40V  
+
VPS  
Linearization circuitry consists of a second, fully inde-  
pendent instrumentation amplifier that controls the bridge  
excitation voltage. It provides second-order correction  
to the transfer function, typically achieving a 20:1  
improvement in nonlinearity, even with low cost trans-  
ducers.  
4-20 mA  
XTR104  
RG  
VO  
RL  
–
The XTR104 is available in 16-pin plastic DIP and  
SOL-16 surface-mount packages specified for the  
–40°C to +85°C temperature range.  
International Airport Industrial Park  
•
Mailing Address: PO Box 11400  
Cable: BBRCORP  
•
Tucson, AZ 85734  
•
Street Address: 6730 S. Tucson Blvd.  
• Tucson, AZ 85706  
Tel: (520)746-1111 Twx: 910-952-1111  
•
•
•
Telex: 066-6491  
•
FAX: (520)889-1510  
•
Immediate Product Info: (800)548-6132  
®
©1992 Burr-Brown Corporation  
PDS-1146B  
Printed in U.S.A. September, 1993  
SPECIFICATIONS  
TA = +25°C, V+ = 24V, and 2N6121 external transistor, unless otherwise noted.  
XTR104BP, BU  
TYP  
XTR104AP, AU  
TYP  
PARAMETER  
CONDITIONS  
MIN  
MAX  
MIN  
MAX  
UNITS  
OUTPUT  
Output Current Equation  
Total Adjusted Error(1)  
Current, Specified Range  
Over-Scale Limit  
Under Scale-Limit  
Full Scale Output Error  
Noise: 0.1Hz to 1kHz  
IO = VIN • (0.016 + 40/RG) + 4mA  
VIN in Volts, RG in Ω  
A
% of FS  
mA  
mA  
mA  
TMIN to TMAX, VFS ≥ 10mV, RB = 5kΩ  
±1  
±2  
*
4
20  
40  
3.8  
±50  
*
34  
3.6  
±15  
8
*
*
*
*
*
*
VIN = 1V, RG = ∞  
±100  
µA  
µAp-p  
R
G = 40Ω  
ZERO OUTPUT(2)  
Initial Error  
vs Temperature  
vs Supply Voltage, V+  
vs Common-Mode Voltage  
VIN = 0V, RG = ∞  
4
±5  
±0.2  
0.5  
0.1  
*
*
*
*
*
mA  
µA  
µA/°C  
µA/V  
µA/V  
±50  
±0.5  
2
±100  
±1  
*
V+ = 9V to 40V(3)  
VCM = 2V to 3V(3)  
2
*
SPAN  
Span Equation (Transconductance)  
Untrimmed Error  
vs Temperature(4)  
Nonlinearity: Ideal Input  
Bridge Input(5)  
S = 0.016 + 40/RG  
*
*
*
A/V  
%
ppm/°C  
%
RG ≥ 75Ω  
±0.1  
±1  
*
±100  
*
±20  
±50  
0.01  
0.1  
*
%
INPUT  
Differential Range  
Input Voltage Range(3)  
Common-Mode Rejection  
Impedance: Differential  
Common-Mode  
1
3
*
*
V
V
dB  
GΩ  
GΩ  
mV  
µV/°C  
dB  
2
80  
*
*
V
IN = 2V to 3V(3)  
100  
3
0.5  
±0.5  
1
130  
100  
0.1  
2
*
*
*
*
2
*
*
*
*
*
Offset Voltage  
vs Temperature  
±2.5  
2.5  
*
5
vs Supply Voltage, V+  
Input Bias Current  
vs Temperature  
Input Offset Current  
vs Temperature  
V+ = 9V to 40V(3)  
110  
*
250  
2
20  
*
*
*
*
nA  
nA/°C  
nA  
0.01  
0.25  
nA/°C  
VOLTAGE REFERENCE(6)  
Voltage  
Accuracy  
vs Temperature  
vs Supply Voltage, V+  
vs Load  
5
±0.25  
±10  
5
*
*
*
*
*
V
%
±0.5  
±50  
±1  
±100  
ppm/°C  
ppm/V  
ppm/mA  
V+ = 9V to 40V(3)  
IL = 0 to 2mA  
50  
POWER SUPPLY  
Voltage Range(3), V+  
9
40  
*
*
V
TEMPERATURE RANGE  
Specification  
Operating  
(TMIN to TMAX  
Derated Performance  
)
–40  
–40  
85  
125  
*
*
*
*
°C  
°C  
θJA  
80  
*
°C/W  
* Specification same as XTR104BP.  
NOTES: (1) Includes corrected second-order nonlinearity of bridge, and over-temperature zero and span effects. Does not include initial offset and span errors which  
are normally trimmed to zero at 25°C. (2) Describes accuracy of the 4mA low-scale current. Does not include input amplifier effects. Can be trimmed to zero.  
(3) Voltage measured with respect to IO pin. (4) Does not include TCR of gain-setting resistor, RG. (5) When configured to correct for ≤2% second-order bridge sensor  
nonlinearity. (6) Measured with RLIN = ∞ to disable linearization feature.  
®
2
XTR104  
PIN CONFIGURATION  
ABSOLUTE MAXIMUM RATINGS  
Power Supply, V+ (referenced to IO pin) .......................................... 40V  
Input Voltage, V+ , V–IN, V+ , V–LIN (referenced to IO pin) ... 0V to V+  
Top View  
DIP  
IN  
LIN  
Storage Temperature Range ........................................ –55°C to +125°C  
Lead Temperature (soldering, 10s) .............................................. +300°C  
Output Current Limit ............................................................... Continuous  
Junction Temperature ................................................................... +165°C  
V+  
V–  
16 Zero Adjust  
15 Zero Adjust  
14 Zero Adjust  
13 B (Base)  
12 VREF  
1
2
3
4
5
6
7
8
IN  
IN  
V+  
LIN  
PACKAGE INFORMATION  
V–  
LIN  
PACKAGE DRAWING  
MODEL  
PACKAGE  
NUMBER(1)  
RG  
RG  
IO  
XTR104AP  
XTR104BP  
XTR104AU  
XTR104BU  
16-Pin Plastic DIP  
16-Pin Plastic DIP  
SOL-16 Surface Mount  
SOL-16 Surface Mount  
180  
180  
211  
211  
11 E (Emitter)  
10 V+  
RLIN  
9
RLIN  
NOTE: (1) For detailed drawing and dimension table, please see end of data  
sheet, or Appendix D of Burr-Brown IC Data Book.  
ORDERING INFORMATION  
TEMPERATURE  
RANGE  
MODEL  
PACKAGE  
XTR104AP  
XTR104BP  
XTR104AU  
XTR104BU  
16-pin Plastic DIP  
16-pin Plastic DIP  
SOL-16 Surface Mount  
SOL-16 Surface Mount  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
ELECTROSTATIC  
DISCHARGE SENSITIVITY  
Electrostatic discharge can cause damage ranging from per-  
formancedegradationtocompletedevicefailure.Burr-Brown  
Corporationrecommendsthatallintegratedcircuitsbehandled  
and stored using appropriate ESD protection methods.  
ESD damage can range from subtle performance degradation  
to complete device failure. Precision integrated circuits may  
be more susceptible to damage because very small parametric  
changes could cause the device not to meet published speci-  
fications.  
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes  
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change  
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant  
any BURR-BROWN product for use in life support devices and/or systems.  
®
3
XTR104  
DICE INFORMATION  
PAD  
FUNCTION  
PAD  
FUNCTION  
1
2
3
4
5
6
7
8
V+  
9
10  
11  
RLIN  
V+  
E (Emitter)  
VREF  
B (Base)  
Zero Adj.  
Zero Adj.  
Zero Adj.  
IN  
V–  
IN  
V+  
LIN  
V–  
12A, 12B  
13  
LIN  
RG  
RG  
IO  
14  
15  
16  
RLIN  
Pads 12A and 12B must be connected.  
NC: No Connection  
Substrate Bias: Internally connected to the IO terminal  
(#7).  
MECHANICAL INFORMATION  
MILS (0.001")  
MILLIMETERS  
Die Size  
Die Thickness  
Min. Pad Size  
168 x 104 ±5  
20 ±3  
4.27 x 2.64 ±0.13  
0.51 ±0.08  
4 x 4  
0.1 x 0.1  
Backing  
None  
XTR104 DIE TOPOGRAPHY  
TYPICAL PERFORMANCE CURVES  
TA = +25°C, V+ = 24V, unless otherwise noted.  
TRANSCONDUCTANCE vs FREQUENCY  
80  
STEP RESPONSE  
60  
40  
RG = 25Ω  
RG = ∞  
RG = 100Ω  
20mA  
R
G = 400Ω  
RG = 25Ω  
RG = 2kΩ  
20  
0
R
G = ∞  
4mA  
100µs/Div  
100  
1k  
10k  
100k  
1M  
Frequency (Hz)  
®
4
XTR104  
TYPICAL PERFORMANCE CURVES (CONT)  
TA = +25°C, +V = 24V, unless otherwise noted.  
COMMON-MODE REJECTION  
vs FREQUENCY (RTI)  
POWER SUPPLY  
REJECTION vs FREQUENCY (RTI)  
120  
100  
80  
140  
120  
100  
80  
G = 0.16A/V  
(RG = 400Ω)  
G = 0.16A/V  
(RG = 400Ω)  
60  
60  
40  
40  
20  
0
20  
0
0.1  
1
10  
100  
1k  
10k  
100k  
0.1  
1
10  
100  
1k  
10k  
100k  
Frequency (Hz)  
Frequency (Hz)  
LOOP RESISTANCE vs LOOP POWER SUPPLY  
OUTPUT CURRENT NOISE DENSITY vs FREQUENCY  
1750  
1500  
1250  
1000  
750  
10  
1550Ω  
(V+) – 9V  
R max =  
20mA  
RG = ∞  
1
Operating  
Region  
500  
250  
0
9V  
0.1  
0
10  
20  
30  
40  
50  
0.1  
1
10  
100  
1k  
10k  
100k  
Loop Power Supply Voltage, VPS (V)  
Frequency (Hz)  
INPUT CURRENT NOISE DENSITY vs FREQUENCY  
INPUT VOLTAGE NOISE DENSITY vs FREQUENCY  
10  
1k  
1
100  
0.1  
10  
0.1  
1
10  
100  
1k  
10k  
100k  
0.1  
1
10  
100  
1k  
10k  
100k  
Frequency (Hz)  
Frequency (Hz)  
®
5
XTR104  
EXTERNAL TRANSISTOR  
APPLICATION INFORMATION  
Transistor Q1 conducts the majority of the signal-dependent  
4 to 20mA loop current. Using an external transistor isolates  
the power dissipation from the precision input and reference  
circuitry of the XTR104, maintaining excellent accuracy.  
Figure 1 shows the basic connection diagram for the XTR104.  
The loop power supply, VPS, provides power for all cir-  
cuitry. Loop current is measured as a voltage across the  
series load resistor, RL.  
Since the external transistor is inside a feedback loop its  
characteristics are not critical. Many common NPN types  
can be used. Requirements for operation at the full loop  
supply voltage are: VCEO = 45V min, β = 40 min and PD =  
800mW. Power dissipation requirements may be lower if the  
maximum loop power supply voltage is less than 40V. Some  
possible choices for Q1 are listed in Figure 1.  
A high impedance (≥2750Ω) strain gage sensor can be  
excited directly by the 5V reference output terminal, VR.  
The output terminals of the bridge are connected to the  
instrumentation amplifier inputs, V+ and V–IN. The resis-  
IN  
tor, RG, sets the gain of the instrumentation amplifier as  
required by the full-scale bridge voltage, VFS.  
The transfer function is:  
(1)  
IO = VIN • (0.016 + 40/RG) + 4mA,  
LOOP POWER SUPPLY  
Where: VIN is the voltage applied to the V+ and  
The voltage applied to the XTR104, V+, is measured with  
respect to the IO connection, pin 7. V+ can range from 9V to  
40V. The loop supply voltage, VPS, will differ from the  
voltage applied to the XTR104 according to the voltage drop  
on the current sensing resistor, RL (plus any other voltage  
drop in the line).  
IN  
V– differential inputs (in Volts.) RG in Ω.  
IN  
With no RG connected (RG = ∞), a 0V to 1V input produces  
a 4 to 20mA output current. With RG = 25Ω, a 0V to 10mV  
input produces a 4 to 20mA output current. Other values for  
RG can be calculated as follows:  
If a low loop supply voltage is used, RL must be made a  
relatively low value to assure that V+ remains 9V or greater  
for the maximum loop current of 20mA. It may, in fact, be  
prudent to design for V+ equal or greater than 9V with loop  
currents up to 34mA to allow for out-of-range input condi-  
tions. The typical performance curve “Loop Resistance vs  
Loop Power Supply” shows the allowable sense resistor  
values for full-scale 20mA.  
2500  
RG  
=
(2)  
1
– 1  
VFS  
Where: VFS is the full scale voltage applied to the V+IN and  
V–IN differential inputs (in Volts).  
RG in Ω.  
Under-scale input voltage (negative) will cause the output  
current to decrease below 4mA. Increasingly negative input  
will cause the output current to limit at approximately  
3.6mA.  
The low operating voltage (9V) of the XTR104 allows  
operation directly from personal computer power supplies  
(12V±5%). When used with the RCV420 Current Loop  
Receiver (see Figure 9), load resistor voltage drop is only  
1.5V at 20mA.  
Increasingly positive input voltage (above VFS) will produce  
increasing output current according to the transfer function,  
up to the output current limit of approximately 34mA.  
12  
VR  
(3)  
RLIN  
1
8
9
RLIN  
V+  
IN  
3
10  
V+  
V+  
LIN  
(3)  
Bridge Sensor  
–
5
RG  
4-20mA  
RG(1)  
13  
11  
(2)  
+
R2  
Q1  
B
E
RB  
XTR104  
0.01µF  
R1  
+
RL  
–
+
VPS  
–
RG  
V–  
6
(3)  
IO  
LIN  
4
2
V–  
7
IN  
2500  
IO = 4-20mA  
(1)  
RG  
=
Ω
Possible choices for Q1 (see text).  
1
– 1  
VFS  
Type  
Package  
TO-225  
TO-220  
TO-220  
where VFS is Full Scale VIN  
.
2N4922  
TIP29B  
TIP31B  
(2) RB ≥ 2750Ω. Otherwise add series resistance (see Figure 8).  
(3) See text — “Linearization”.  
FIGURE 1. Bridge Sensor Application, Connected for Positive Nonlinearity.  
®
6
XTR104  
BRIDGE BALANCE  
With V+  
and V–  
connected to the bridge output, the  
LIN  
LIN  
bridge excitation voltage can be made to vary as much as  
±0.5V in response to the bridge output voltage. Be sure that  
the total load on the VR output is less than 2mA at the  
maximum excitation voltage, VR = 5.5V.  
Figure 1 shows a bridge trim circuit (R1, R2). This adjust-  
ment can be used to compensate for the initial accuracy of  
the bridge and/or to trim the offset voltage of the XTR104.  
The values of R1 and R2 depend on the impedance of the  
bridge, and the trim range required. This trim circuit places  
an additional load on the VR output. The effective load of the  
trim circuit is nearly equal to R2. Total load on the VR output  
terminal must not exceed 2mA. An approximate value for R1  
can be calculated:  
Signal-dependent variation of the bridge excitation voltage  
provides a second-order term to the complete transfer func-  
tion (including the bridge). This can be tailored to correct for  
bridge sensor nonlinearity. Either polarity of nonlinearity  
(bowing up or down) can be compensated by proper connec-  
tion of the VLIN inputs. Connecting V+LIN to V+IN and V–  
5V • R B  
LIN  
to V–IN (Figure 1) causes VR to increase with bridge output  
which compensates for a positive bow in the bridge re-  
sponse. Reversing the connections (Figure 3) causes VR to  
decrease with increasing bridge output, to compensate for  
negative-bowing nonlinearity.  
(3)  
R1  
≈
4 • V TRIM  
Where: RB is the resistance of the bridge.  
TRIM is the desired ±voltage trim range (in V).  
V
Make R2 equal or lower in value to R1.  
To determine the required value for RLIN you must know the  
nonlinearity of the bridge sensor with constant excitation  
voltage. The linearization circuitry can only compensate for  
the parabolic portion of a sensor’s nonlinearity. Parabolic  
nonlinearity has a maximum deviation from linear occurring  
at mid-scale (see Figure 4). Sensors with nonlinearity curves  
similar to that shown in Figure 4, but not peaking exactly at  
mid-scale can be substantially improved. A nonlinearity that  
is perfectly “S-shaped” (equal positive and negative  
nonlinearity) cannot be corrected with the XTR104. It may,  
however, be possible to improve the worst-case nonlinearity  
of a sensor by equalizing the positive and negative  
nonlinearity.  
Figure 2 shows another way to adjust zero errors using the  
output current adjustment pins of the XTR104. This pro-  
vides ±500µA (typical) adjustment around the initial low-  
scale output current. This is an output current adjustment  
that is independent of the input stage gain set with RG. If the  
input stage is set for high gain the output current adjustment  
may not provide sufficient range.  
(a)  
XTR104  
14  
The nonlinearity, B (in % of full scale), is positive or  
negative depending on the direction of the bow. A maximum  
of ±2.5% nonlinearity can be corrected. An approximate  
value for RLIN can be calculated by:  
15  
16  
10kΩ  
±500µA typical  
output current  
adjustment range.  
K LIN • V FS  
(5)  
RLIN  
=
0. 2 • B  
(b)  
Where: KLIN ≈ 24000.  
XTR104  
VFS is the full-scale bridge output (in Volts) with  
constant 5V excitation.  
B is the parabolic nonlinearity in ±% of full scale.  
RLIN in Ω.  
14  
15  
16  
5kΩ  
5kΩ  
±50µA typical  
output current  
adjustment range.  
Methods for refining this calculation involve determining  
the actual value of KLIN for a particular device (explained  
later).  
FIGURE 2. Low-scale Output Current Adjustment.  
B is a signed number (negative for a downward-bowing  
nonlinearity). This can produce a negative value for RLIN. In  
this case, use the resistor value indicated (ignore the sign),  
LINEARIZATION  
Differential voltage applied to the linearization inputs, V+  
and V–LIN, causes the reference (excitation) voltage, VR, to  
vary according to the following equation:  
LIN  
but connect V+  
Figure 3.  
to V– and V–  
to V+ as shown in  
LIN  
IN  
LIN IN  
This approximate calculation of RLIN generally provides  
about a 5:1 improvement in bridge nonlinearity.  
KLIN  
(4)  
V R = 5V + V LIN  
R LIN  
Example: The bridge sensor depicted by the negative-  
bowing curve in Figure 4. Its full scale output is 10mV with  
constant 5V excitation. Its maximum nonlinearity, B, is  
–1.9% referred to full scale (occurring at mid-scale). Using  
equation 5:  
Where: VLIN is the voltage applied to the V+ and V–  
LIN  
LIN  
differential inputs (in V).  
RLIN in Ω.  
KLIN ≈ 24000 (approximately ±20% depending on  
variations in the fabrication of the XTR104).  
®
7
XTR104  
12  
VR  
RLIN  
1
3
8
V+  
9
RLIN  
IN  
(1)  
10  
V+  
V+  
LIN  
Bridge Sensor  
–
5
RG  
4-20mA  
13  
11  
RG  
+
R2  
0.01µF  
B
E
RB  
XTR104  
R1  
+
RL  
–
+
VPS  
–
RG  
V–  
6
IO  
LIN  
(1)  
4
2
V–  
7
IN  
IO = 4-20mA  
NOTE: (1) VLIN inputs connected for negative nonlinearity (B < 0).  
Pins 3 and 4 must be reversed for B > 0 (see Figure 1).  
FIGURE 3. Bridge Sensor, VLIN Connected for Negative Nonlinearity.  
24000 • 0. 01  
RLIN  
≈
= −632 Ω  
0. 2 • (−1. 9)  
Use RLIN = 632Ω. Because the calculation yields a negative  
result, connect V+ to V– and V– to V+  
BRIDGE TRANSDUCER TRANSFER FUNCTION  
WITH PARABOLIC NONLINEARITY  
10  
.
IN  
LIN  
IN  
LIN  
9
8
Gain is affected by the varying the excitation voltage. For  
each 1% of corrected nonlinearity, the gain must be altered  
by 4%. As a result, equation 2 will not provide an accurate  
RG when nonlinearity correction is used. The following  
equation calculates the required value for RG to compensate  
for this effect.  
Positive Nonlinearity  
7
B = +2.5%  
6
5
4
B = –1.9%  
Negative Nonlinearity  
3
2500  
2
Linear Response  
RG  
=
(6)  
1
0
1
− 1  
(1 + 0. 04 • B) V FS  
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  
Normalized Stimulus  
1
B must again be a signed number in this calculation—  
positive for positive bowing nonlinearity, and negative for a  
negative-bowing nonlinearity.  
NONLINEARITY vs STIMULUS  
RG = 23.32Ω for the example above.  
3
2
A more accurate value for RLIN can be determined by first  
measuring the actual gain constant of the linearization in-  
puts, KLIN (see equation 4). Measure the change in the  
reference voltage, ∆VR, in response to a measured voltage  
change at the linearization inputs, ∆VLIN. Make this mea-  
surement with a known, temporary test value for RLIN. These  
measurements can be made during operation of the circuit  
by providing stimulus to the bridge sensor, or by temporarily  
unbalancing the bridge with a fixed resistor in parallel with  
Positive Nonlinearity  
B = +2.5%  
1
0
–1  
–2  
–3  
Negative Nonlinearity  
B = –1.9%  
one of the bridge resistors. Calculate the actual KLIN  
:
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  
Normalized Stimulus  
1
∆ V R • R TEST  
(7)  
K LIN  
=
∆ VLIN  
FIGURE 4. Parabolic Nonlinearity.  
Where: ∆VLIN is the change in voltage at VLIN  
.
∆VR is the measured change in reference voltage, VR.  
RTEST is a temporary fixed value of RLIN (in Ω).  
®
8
XTR104  
Then, RLIN can be calculated using equation 5 using the  
accurate value of KLIN from equation 7. KLIN can be a  
different value for each XTR104.  
OTHER SENSOR TYPES  
The XTR104 can be used with a wide variety of inputs. Its  
high input impedance instrumentation amplifier is versatile  
and can be configured for differential input voltages from  
millivolts to a maximum of 1V full scale. The linear com-  
mon-mode range of the inputs is from 2V to 4V, referenced  
to the IO terminal, pin 7.  
It is also possible to make a real-time adjustment of RLIN  
with a variable resistor (active circuit trimming). This is  
done by measuring the change in VR in response to a zero-  
to-VFS change in voltage applied to the VLIN inputs. To  
correct for each 1% of nonlinearity, the excitation voltage,  
VR, must make a 4% change at full-scale input. So the  
change in reference voltage, ∆VR, for a full-scale change in  
VLIN can be calculated by:  
You can use the linearization feature of the XTR104 with  
any sensor whose output is ratiometric with an excitation  
voltage. For example, Figure 5 shows the XTR104 used with  
a potentiometer position sensor.  
∆VR = 0.2 • B  
(8)  
REVERSE-VOLTAGE PROTECTION  
Example: A bridge sensor has a –1.9% nonlinearity. Apply  
the full-scale bride output, VFS (10mV), to the VLIN inputs  
and adjust RLIN for:  
Figure 6 shows two ways to protect against reversed output  
connection lines. Trade-offs in an application will determine  
which technique is better. D1 offers series protection, but  
causes a 0.7V loss in loop supply voltage. This may be  
undesirable if V+ can approach the 9V limit. Using D2  
(without D1) has no voltage loss, but high current will flow  
in the loop supply if the leads are reversed. This could  
damage the power supply or the sense resistor, RL. A diode  
with a higher current rating is needed for D2 to withstand the  
highest current that could occur with reversed lines.  
VR'’ = 5V + 0.2 • B = 4.62V  
Note that with all the calculation and adjustment methods  
described above, the full-scale bridge output is no longer  
equal to VFS because the excitation voltage at full scale is no  
longer 5V. All the calculations and adjustment procedures  
described above assume VFS to be the full-scale bridge  
output with constant 5V excitation. It is not necessary to  
iterate the calculations or adjustment procedures using the  
new full-scale bridge output as a starting point. However, a  
new value for RG must be calculated using equation 6.  
SURGE PROTECTION  
Long lines may be subject to voltage surges which can  
damage semiconductor components. To avoid damage, the  
maximum applied voltage rating for the XTR104 is 40V. A  
zener diode can be used for D2 (Figure 7) to clamp the  
voltage applied to the XTR104 to a safe level. The loop  
power supply voltage must be lower than the voltage rating  
of the zener diode.  
A refined value for RLIN, arrived at either by active circuit  
trimming, or by measuring linearization gain (equation 7)  
will improve linearity. Reduction of the original parabolic  
nonlinearity of the sensor can approach 40:1. Actual results  
will depend on higher-order nonlinearity of the sensor.  
There are special zener diode types (Figure 7) specifically  
designed to provide a very low impedance clamp and with-  
stand large energy surges. These devices normally have a  
diode characteristic in the forward direction which also  
If no linearity correction is desired, make no connections to  
the RLIN pins (RLIN = ∞). This will cause the VR output to  
remain a constant +5V. The V+ and V– inputs should  
remain connected to the bridge output to keep these inputs  
biased in their active region.  
LIN  
LIN  
5V  
12  
RLIN  
8
VR  
1
9
V+  
V+  
RLIN  
8kΩ  
IN  
10  
V+  
3
5
LIN  
2.5V  
to  
3V  
RG  
4-20 mA  
13  
2.5kΩ  
RG  
B
0.01µF  
XTR104  
2kΩ  
+
RL  
–
+
VPS  
–
6
E
RG  
V–  
11  
10kΩ  
IO  
LIN  
4
2
V–  
10kΩ  
7
IN  
2.5V  
10kΩ  
FIGURE 5. Potentiometer Sensor Application.  
®
9
XTR104  
protects against reversed loop connections. As noted earlier,  
reversed loop connections would produce a large loop cur-  
rent, possibly damaging RL.  
Bypass capacitors on the input often reduce or eliminate this  
interference. Connect these bypass capacitors to the IO  
terminal (see Figure 7). Although the DC voltage at the IO  
terminal is not equal to 0V (at the loop supply, VPS) this  
circuit point can be considered the transmitter’s “ground”.  
RADIO FREQUENCY INTERFERENCE  
The long wire lengths of current loops invite radio frequency  
interference. RF can be rectified by the sensitive input  
circuitry of the XTR104 causing errors. This generally  
appears as an unstable output current that varies with the  
position of loop supply or input wiring.  
LOW-IMPEDANCE BRIDGES  
Low impedance bridges can be used with the XTR104 by  
adding series resistance to limit excitation current to ≤2mA.  
Equal resistance should be added to the upper and lower  
sides of the of the bridge (Figure 8) to keep the bridge output  
voltage centered at approximately 2.5V. Bridge output is  
reduced, so a preamplifier, as shown, may be needed to  
reduce offset and drift.  
If the bridge sensor is remotely located from the XTR104,  
the interference may enter at the input terminals. For inte-  
grated transmitter assemblies with short connections to the  
sensor, the interference more likely comes from the current  
loop connections.  
1N4148  
D1  
Use either D1 or D2.  
See “Reverse Voltage Protection.”  
10  
V+  
0.01µF  
13  
B
D2  
1N4001  
XTR104  
E
RL  
VPS  
11  
IO  
7
FIGURE 6. Reverse Voltage Protection.  
Zener diode 36V: 1N4753A  
or  
General Semiconductor Transorb™ 1N6286A, special  
low impedence clamp type. Use lower voltage zener  
diodes with loop power supply voltages less than 30V  
for increased protection.  
12  
VR  
RLIN  
1
3
8
V+  
9
RLIN  
IN  
10  
V+  
V+  
LIN  
Bridge  
Sensor  
5
RG  
4-20mA  
13  
11  
RG  
–
+
Q1  
D2  
B
E
RB  
XTR104  
+
RL  
–
+
VPS  
–
RG  
V–  
6
0.01µF  
IO  
LIN  
4
2
V–  
7
IN  
IO = 4-20mA  
Maximum VPS must be less than  
minimum voltage rating of zener diode.  
0.01µF  
0.01µF  
FIGURE 7. Over-Voltage Surge Protection.  
®
10  
XTR104  
1.37mA at 5V  
≈ 400µA  
1.65kΩ  
RLIN  
10  
+
–
1kΩ  
1N4148  
0.01µF  
12  
1
V+  
V+  
8
LT1049  
IN  
VR  
9
LIN  
3
5
V+  
RG  
90kΩ  
RG  
25Ω  
13  
XTR104  
B
E
1µF  
350Ω  
6
4
RG  
V–  
IO  
11  
9.4kΩ  
LIN  
V–  
7
IN  
2
IO = 4-20mA  
1.65kΩ  
Bridge Excitation  
Voltage = 0.42V  
approx. x10  
Amplifier  
FIGURE 8. 350Ω Bridge With X10 Preamplifier.  
+12V  
RLIN  
12  
1
1N4148  
8
V+  
IN  
9
VR  
10  
V+  
V+  
1µF  
Bridge Sensor  
LIN  
3
RG  
5
13  
0.01µF  
XTR104  
B
E
RG  
–
+
16  
RB  
10  
6
4
RG  
V–  
11  
3
2
IO  
11  
12  
LIN  
7
VO = 0 to 5V  
V–  
15  
14  
IN  
RCV420  
2
IO = 4-20mA  
13  
5
4
1µF  
–12V  
FIGURE 9. ±12V-Powered Transmitter/Receiver Loop.  
RLIN  
12  
1N4148  
+15V  
1
8
V+  
V+  
1µF  
1µF  
IN  
9
VR  
10  
V+  
Isolated Power  
from PWS740  
Bridge  
Sensor  
0
LIN  
3
5
RG  
13  
–15V  
0.01µF  
XTR104  
B
E
RG  
–
+
16  
10  
11  
RB  
6
4
RG  
V–  
V–  
3
2
IO  
11  
12  
LIN  
V+  
7
1
15  
14  
IN  
RCV420  
2
9
15  
I
O = 4-20mA  
7
8
13  
ISO122  
VO  
5
4
0 – 5V  
10  
2
16  
V–  
FIGURE 10. Isolated Transmitter/Receiver Loop.  
®
11  
XTR104  
厂商 型号 描述 页数 下载

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 		XTR101AG 高精度，低漂移的4-20mA两线制变送器[ Precision, Low Drift 4-20mA TWO-WIRE TRANSMITTER ] 25 页

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