18
Introduction to 4-20mA Current Loop Transmitters TI Precision Labs – Current Loop Transmitters Presented by Katlynne Jones Prepared by Katlynne Jones 1
Introduction to 4-20mA Current Loop Transmitters TI Precision Labs – Current Loop Transmitters
Presented by Katlynne Jones
Prepared by Katlynne Jones
1
Current transmitter applications
2
ValveControl Station
Heater
Level
Sensor
Temp
Sensor
Ambient light, temperature,
& humidity sensors
Lighting, HVAC,
& humidity control
Control Station
Industrial automation Building automation
4-20mA overview
• 4mA represents 0% input level – Allows up to 4mA to power external input circuitry
– 4mA zero level allows under-scale settings and fault detection
• 20mA represents 100% input level – Over-scale can also be used to detect fault conditions
Sensor
Receiver
250Ω
0 to 100%
Signal
4 to 20mA
Signal
Transmitter 1 to 5V0 to 150°C
3
4-20mA overview
• 4mA represents 0% input level – Allows up to 4mA to power external input circuitry
– 4mA zero level allows under-scale settings and fault detection
• 20mA represents 100% input level – Over-scale can also be used to detect fault conditions
Failure OK Failure
213.60 mA
4
Transmitter configurations
5
Transmitter
+
_
+
_
Receiver
Power
supply
Supply &
Signal Current
VLOOP
1
2
+
_
Power
supply
+
_
Receiver
Transmitter
Supply
Current
Signal
Current
1
2
3
4
2-wire block diagram 3-wire block diagram 4-wire block diagram
+
_
Power
supply
+
_
Receiver
Transmitter
Supply
Current
Signal
Current
1
2
3
5
Field Control Station
Receiver
250Ω
Wiring
Resistance
+_
+_
4-20mA
Transmitter
Supply
24V
ADC+_
Why use current transmitters?
6
• Current transmission block diagram
– Transmitter: current
source
– Receiver: 250Ω resistor
translates current to
voltage
– ADC: translates voltage
to digital signal
Field Control Station
Receiver
250Ω
Wiring
Resistance
+_
+_
4-20mA
Transmitter
Supply
24V
ADC
>1km
+_
+_
+_
Why use current transmitters?
7
• Current transmission block diagram
– Signals travel >1km
– Voltage transmission
would be attenuated
– Current loops are
essentially lossless
Field Control Station
Receiver
250Ω
Wiring
Resistance
+_
+_
4-20mA
Transmitter
Supply
24V
ADC
+_
+_
+_
Current
Why use current transmitters?
8
• Current transmission block diagram
– Current in a loop is
equivalent at any point in
the loop
– Current leakage can
introduce error 8mA
8mA
Field Control Station
Receiver
250Ω
+_
+_
4-20mA
Transmitter
Supply
24V
ADC+_
Current
Non-ideal
Resistance
Leakag
e
Why use current transmitters?
9
• Current transmission block diagram
– Current in a loop is
equivalent at any point in
the loop
– Current leakage can
introduce error 8mA
8mA
Field Control Station
Receiver
250Ω
Wiring
Resistance
+_
+_
4-20mA
Transmitter
Supply
24V
ADC
>1km
+_
+_
+_
Environmental
Noise Source
Environmental
Noise Source
Why use current transmitters?
10
• Current transmission block diagram
– Many noise sources in
industrial environments
– Low impedance of a
current loop system
makes it much less
sensitive to induced
noise
11
How are analog outputs used in industrial automation?
• Programmable logic controllers (PLCs) – Analog output modules that control
something placed in the field • Communication, valve position, position
of linear actuator, etc.
– Analog output module is powered by PLC back-plane • Primarily 3-wire systems
• Field elements –Analog outputs paired with sensors,
placed remotely in the field
–Comprise a majority of the market for industrial analog outputs
–Most often 2-wire, or loop-powered, 4-20mA sensor transmitters
°T
3-Wire
Transmitter
2-Wire
Transmitter
RVLOOP
Typical 4-20mA applications
12
– Temperature
– 2-wire transmitter
– Valve, heater
– 3-wire transmitter
Transmit control
signals from a
control station out to
a remote device.
Report a process
variable from a
remote sensor to a
control station.
Designing 4-20mA transmitters
• Discrete
– Customizable
• Partially integrated
– Reduces size while still allowing for various input types
• Fully integrated
– Further reduces size
– HART interface
13
4-20mA transmitters – fully discrete
14
TIPD102
TIPD158
DACA1
R1
R2
+
R4 R3
VREG
Regulator
R5
Loop+
Loop-
Q1
VDAC
U1
RIN
+
2475Ω
VREG_5V V+
IO
Q1
V+
Q1
E
B
5V
Regulator
4.096V
Reference
25Ω
VREF_4.096V
IIN
IRET RLIM
10 nF
XTR116
Loop+
Loop-
+
-
Ref
+
INA333
143kΩ
19.6kΩ
RG2.55kΩ10kΩ
12.49kΩ
OPA333
+
-
+
VREF_4.096V
VREF_4.096V
VREG_5V
VREF_0.5V
RADJUST
50Ω
RCOMP
10pF
CHF
10pF
CLF
IRET
IRET
IRET
10nF
10nF
4-20mA transmitters – partially integrated
15
TIPD190
TIPD155
SCLK
SDO
SDIN
DVDDREFOUT REFIN LP_X
IRANGE
IENABLE
LDAC
DAC Input Register
SP
I S
hift R
egis
ter
Input
Co
ntr
ol Logic
DAC IAmp
VSENSEP_X
VENABLE
CCOMP_X
User Calibration
Register
Slew Rate Control
Internal Reference
X
Buck/Boost Converters
Watchdog Timer
Alarm
PVDD_X LN_X VPOS_IN_X
AGND1
AVDD
VAmp
Feedback
CHANNEL - A
CHANNEL - B
CHANNEL - C
CHANNEL - D
VNEG_IN_X
PVSS_X
DVDD_EN
Amp
Power On Reset
HARTIN_X
Current Source
CLR
SYNC
RESET
ALARM
AGND2 AGND3
Σ
HART Filters
GND
IOUT
VOUT
or
AVDD
4-20mA transmitters – fully integrated
16
TIPD119
TIPD216
HART – what is it? why is it useful?
• HART – Highway Addressable Remote Transducer
– Bell 202 Frequency Shift Keying Standard at 1200 bps
• “Mark” and “Space” symbols (1mApp)
– Mark: 1200 Hz sinusoid, represents 1
– Space: 2200 Hz sinusoid, represents 0
17
4mA
20mA
Time
4-20mA “DC” signal
only communicates a
single variable, typically
sensor data
4mA
20mA
0
1
0
1
0
1
Time
4-20mA “DC” signal
communicates primary
variable, sensor data
HART FSK signals communicate auxiliary information such as
in-system calibration data, reliability information / diagnostics,
and additional sensor data
“Simple” sensor transmitter “Smart” sensor transmitter
18
Thanks for your time!
Please try the quiz.
