Download 4-20mA 2_3 Wire

2-Wire XTR Products
NOT FOR
3-Wire XTR Applications
1
4 to 20mA Current Loop
Needs only 2 Wires
(normally loosely twisted, sometimes shielded)
for all of these functions:
1. Sensor Excitation
2. Signal Conditioning
3. Signal Transmission
jm-Sept 05
2
4 to 20mA Current Loop
Supply
Voltage
XTR
Sensor
Sensor
Signal
Conditioning
XTR
VS
Signal
Converter
and
Supply
X
Signal
Receivers:
VS=I*R
RCV1
Signal
Current
Output
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RCV2
RCV n
3
4 to 20mA Current Loop
Supply Voltage
XTR
• Supply Voltage nominal 24V
• Min: +12V (sometimes as low as +7V)
• Max: +36V (short time over-voltage +40V)
Power supply for the XTR and the Sensor is
derived from the minimum current <4mA
(<3.4mA) and the sub-regulated supply
voltage.
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4
4 to 20mA Current Loop
Standard Specification
XTR
• Signal Current Range: 4.0 to 20.0mA
• Error Signaling Range: 3.4 to 4mA and 20 to 24mA
These under and over ranges are used to indicate error
conditions of the sensor: wire break, short, over-load,
excitation failure. There is a “NAMUR” specification,
which specifies these special ranges.
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5
4 to 20mA Current Loop
Power Dissipation
XTR
• Power dissipation of the XTR is calculated from
the voltage across the XTR and the current
flowing.
• Examples:
24Vsupply – (20mA*500W) = 14V
P = 14V * 20mA = 280mW
36Vsupply – (20mA*50W) = 35V
P = 35V * 20mA = 700mW
We use an external power transistor to get the
heat out of the IC.
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6
4 to 20mA Current Loop
Circuit Protection
XTR
Protection against harsh industrial
environment:
+ Supply
XTR
Signal Out
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7
4 to 20mA Current Loop
Why “Current”
XTR
Constant current generates a constant voltage across a
“Shunt” resistor
–
–
–
–
–
–
Insensitive to wire resistance
Insensitive to multiple receivers (shunts)
Insensitive to conducted noise
Easy signal filtering
Low cost wiring ( just 2 wires)
Used in Industry since many years
It will remain STANDARD for many years, because:
– Lower cost than digital signal transmission
– Better noise immunity
– Longer distance ( >1km)
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8
4 to 20mA Current Loop
HART Protocol
XTR
• HART is a digital protocol which can be
modulated onto the 4 to 20mA signal
wires.
• It is used where remote sensor
programming is required (“Smart Sensor”)
• HART puts several restrictions to the
wiring, wire length, shunt resistance and
supply voltage.
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9
3-Wire Connection
Supply
Voltage
XTR
Sensor
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Sensor
Signal
Conditioning
Signal
Converter
(and
Supply)
Signal
Signal
Receiver
12
Current or Voltage Transmitter
XTR
• Many sensors are connected via 3 Wires:
+Supply, GND, Signal
Do not mix with the 2-wire 4 to 20mA current loop !
Popular signals for these active sensors are:
“V” 0 to +10V, 0 to +5V
“I” 0 to +20mA ( 24mA ), 4 to 20mA ( 3.4 to 24mA )
The current signal is compatible to the “4 to 20mA
current loop” signals.
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13
3-Wire Current Transmitter
XTR
• XTR110 (“old” product)
• XTR111 ( New Product in planning !)
+24V
Output
Disable
Reg.
Out
I-Mirror
DRV
Output
Failure
-
SENSE
+
VREF
Signal
Input
I1
IOUT
+
-
0 to 20mA
(4 to 20mA)
GND
IOUT = VIN/RSET * 10
RSET
IOUT = 10*I1
jm-Sept 05
• External Resistor R1 allows
flexible setup to a wide range of
output currents.
• Supply max : 44V, nominal: 24V.
• Supply min: < 9V
• Current compliance stretches well
below GND ( external transistor)
• I1 defined by ext. R1. I2 = 10 * I1
• Regulator output: <5mA
• Package: DFN-10 [3x3mm]
• Internet Price: $1.45 (@1kpcs)
• RTM: Q2 2006
14
3-Wire Voltage Transmitter
Discrete solution
Supply
Voltage
(PGA309 ...)
Sensor
Sensor
Signal
Conditioning
“XTR”
Signal
+
OPA
-
Signal
Receiver
Driver Op Amp
(and Supply)
R2 1k
R1 1k
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16
3-wire Transmitter
Current or Voltage Output
“XTR”
digitally selectable
Supply
Voltage
(PGA309 ...)
Sensor
Sensor
Signal
Conditioning
Signal
XTR300
Signal
Receiver
XTR300
and Supply
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17
Normal 2-Wire Operation of XTR115
Input Signals & Feedback Voltage, VR2, referenced to Iret
Feedback Voltage, VR2 is negative with reference to Iret
Op Amp Circuit Loop Gain forces A1+ = A1- = Iret = 0V
IIN = VIN / RIN + Vref / Roffset
IR1 = IIN
IIN * R1 = VR2
VR2 = Iout / R2, Op Amp Loop Controls Iout to Create VR2
Iout = VR2 /R2
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18
3-Wire 4-20mA NOT for XTR115 (or any 2-Wire XTR!)
Current cannot flow through R2 in the right direction to create 0V at A1+
(Need VR2 to be negative referenced to Iret)
T1 drives current into ground at Iout over-current limit of 41mA
tg-Sept
05 though RL !!
No current
19
4-20mA Transmitter Design Solutions

2-Wire General Purpose

3-Wire General Purpose

4-20mA Current Loop Receiver

2-Wire RTD Conditioners
with Linearization

2-Wire Bridge Sensor Conditioners
with Linearization

2-Wire RTD Conditioner
with Digital Cal (Linearization, Span, Offset)
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20
2-Wire General Purpose
Sensor
Excitation
Loop
Voltage
(V)
Full-Scale
Input
Range
5mV to
1V
Output
Range
(mA)
Additional
Power
Available
Package
Price
1k
$USD
4-20
---
DIP-14
SOIC-16
7.34
Device
Description
XTR101
IA + Current
Excitation
Two 1 mA
11.6 to
40
XTR115
IIN to IOUT Converter.
External Resistor
Scales VIN to IIN.
VREF=2.5V
7.5 to
36
40μA to
200μA
4-20
5V@4mA
SOIC-8
0.95
XTR116
IIN to IOUT Converter.
External Resistor
Scales VIN to IIN.
VREF=4.096V
7.5 to
36
40μA to
200μA
4-20
5V@4mA
SOIC-8
0.95
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XTR115 / XTR116
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22
3-Wire General Purpose
Device
Description
XTR110
Selectable
Input/Output
Ranges
Sensor
Excitation
VREF=10V
Loop
Voltage
(V)
FullScale
Input
Range
13.5 to 40
0V to 5V
0V to 10V
Output
Range
(mA)
Additiona
l
Power
Available
Package
Price
1k
$USD
4-20,
0-20,
5-25
---
DIP-16
6.35
XTR110
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23
4-20mA Current Loop Receiver
Device
Description
RCV420
4-20mA input,
0-5V Output,
1.5V Loop Drop
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Sensor
Excitation
Loop
Voltage
(V)
Full-Scale
InputRange
(mA)
Output
Range
(V)
Additional
Power
Available
Package
Price
1k
$USD
VREF=10V
+11.5/-5 to
+/-18
4-20
0-5V
---
DIP-16
3.34
24
2-Wire RTD Conditioner with Linearization
Device
Description
XTR105
100Ω RTD
Conditioner
XTR112
1kΩ RTD
Conditioner
XTR114
10kΩ RTD
Conditioner
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Sensor
Excitation
Loop
Voltage
(V)
Two 800μA
7.5 to
36
Two 250μA
7.5 to
36
Two 100μA
7.5 to
36
Full-Scale
Input
Range
5mV to 1V
5mV to 1V
5mV to 1V
Output
Range
(mA)
4-20
4-20
4-20
Additional
Power
Available
Package
Price
1k
$USD
5.1V@1mA
DIP-14
SOIC-14
3.75
5.1V@1mA
DIP-14
SOIC-14
3.75
5.1V@1mA
DIP-14
SOIC-14
3.75
25
2-Wire Bridge Sensor Conditioner
with Linearization
Device
Description
Sensor
Excitation
Loop
Voltage
(V)
XTR106
Bridge
Conditioner
5V and 2.5V
7.5 to 36
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Full-Scale
Input
Range
Output
Range
(mA)
Additional
Power
Available
Package
Price
1k
$USD
5mV to 1V
4-20
5.1V@1mA
DIP-14
SOIC-14
3.75
26
2-Wire RTD Conditioner
with Digital Cal for Linearization, Span, Offset
Device
Description
Sensor
Excitation
XTR108
100Ω to 1kΩ RTD
Conditioner
w/6-Channel Input Mux.
Extra Op Amp can
convert to Voltage
Sensor Excitation.
Two 500μA
Programmable
tg-Sept 05
Loop
Voltage
(V)
Full-Scale
Input
Range
Output
Range
(mA)
7.5 to
24
5mV to
320mV
4-20
Additional
Power
Available
Package
Price
1k
$USD
5.1V @
2.1mA
SSOP-24
3.75
27
RTD IN & 4-20mA OUT w/Digital Calibration
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XTR108 Key Features
• 10Ω to 10kΩ RTD Conditioner
• RTD Compensation
 Offset, Span, NonLinearity
• 0.1% Post-Calibration Accuracy
• -40°C to +85°C Range
• Loop Voltage: 7.5V to 40V
• SPI Interface Digital Calibration/Configuration
• 6 Channel Input Mux
 Allows for up to 5 different Zero set points
• Internal/External VREF
• Undedicated Spare Op Amp
• Uses Standard External SPI 1k EEPROM (8-SOIC Package)
• Can be used in 3-Wire 4-20mA systems (Voltage Out Mode)
• 5.1V Sub-Regulated Output
• SSOP-24 Package
• $3.35 @1k
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29
XTR108EVM & Development Tools
XTR108EVM Control/Program Software
XTR108 Resistor Selection Tool
XTR108EVM User’s uide
XTR108 QuickStart Guide
Detailed, Step-by-Step System Calibration “Definition by Example”
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30
New & Improved XTR108EVM
4-20mA
Loop
Isolation from
Ground to Iret
Programming Board
Transmitter Board
Evaluate XTR108 with your RTD
Software Calibration/Control for XTR108
Available NOW!
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31
XTR108 Modification for
3-Wire Voltage (or Current) Output
XTR108: PTC [PT10 – PT10000] Sensor Front-End
VOUT
See NEW data sheet for details (page25)
jm-Sept 05
32
XTR117, 4-20mA Transmitter










High Accuracy: Low Span & Offset Errors
Easily interfaced with sensors or circuitry
Simple Over-Scale signaling
Regulated 5V power for External Circuitry
Minimal power consumption: 250µA
Wide Operating Voltage range: +7.5V to +40V
Tolerant of power supply surges up to +50V
Gain of 100x to reduce noise sensitivity
Miniature MSOP-8 package
$0.90USD @ 1k Qty
VREG
RIN
Sensor
Sensor
Condition
Circuit
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XTR117
+5V
Linear
SubReg






Accuracy without calibration
Noise resistant signaling
Robust in harsh electrical environments
A generous 3.75mA available for sensor circuitry
Requires minimal board space
Unbeatable: Cost/Size/Performance benefits
 Pressure Transducers
 Temperature Transducers
 Humidity Transducers
 Industrial Process Monitors
 PGA309 4-20mA Output Converter
(Convert Voltage-Out to Current-Out)
V+
IIN
VLOOP
7.5V to 40V
A1
VIN
RL
IRET
IOUT
IOUT = 100 * VIN/RIN
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Complete 4-20mA Sensor Conditioner
Digital Calibration of Sensor Linearity, Span, Offset, Tempcos
PGA308
VS
&
XTR117
T
VREG
+
P
Non-Linear
psi
0
50
PGA309
Bridge
Transducer
VEXC
-
Linearization
DAC
RIN
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Linear VOUT
VLOOP
7.5V to 40V
VIN
RL
IRET
Analog Signal Conditioning
DIGITAL CAL
Int
Int
Temp
Temp
Ext Temp
V+
A1
Over/Under
Over/Under
Scale
Scale Limiter
Limiter
+
Ext
Temp
Linear
SubReg
IIN
Auto - Zero
PGIA
Digital
Temperature
Compensation
+5V
Ref
Ref
Linearization
Linearization
Ckt
Ckt
Analog Sensor Linearization
Fault
Fault
Monitor
Monitor
XTR117
Temp
ADC
Control Register
Interface Circuitry
EEPROM
(SOT23-5)
IOUT
IOUT = 100 * VIN/RIN
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