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3–201
Motorola Sensor Device Data
For More Information On This Product,
Go to: www.freescale.com
4
2
3
6
Figure 1. Demo Kit with 4–20 mA Current Loop
R4
VCC = +15 Volts dc
C1
C2
R8
R9
RL
R7
R6
R3
R5
R12
R10
R11
Roff
OFFSET ADJUST
a 3
–
2N2222
+
–
–
+
+
+
a 1
a 2
4
7
R2
R1
5
8
1
2
3
RG
gain
adj.
1
MPX2100DP
output
Basic Circuit of SEK–1
Additional Circuit for 4 to 20 mA current loop
(Receiver Load Resistance : RL = 150 to 400 Ohms)
RG = 47 K Pot.
Roff = 1 MPot.
*R1 = R2 = 330 KR11 = 1 M
*R3 = R4 = 27 K R12 = 330 K
*R5 = R6 = 27 K C1 = C2 = 0.1
μ
F
*R8 = R9 = 150 a1, a2, a3 = 1/4 MC33079
*All resistor pairs must be matched at better than 0.5%
R7 = 1 K
R10 = 110 K
Note A: If using SEK–1 a1, a2, a3 = 1/2 MC33078
Note A:
RG from20 K to 47 K
Note A:
R1 and R2 from1Mto 330 K
NOTICE: THE PRESSURE SENSOR OUTPUT IS RATIOMETRIC TO THE POWER SUPPLY
VOLTAGE. THE OUTPUT WILL CHANGE WITH THE SAME RATIO AS VOLTAGE CHANGE.
Remote
Receiver
–
The output is ratiometric to the power supply voltage. For
example, if the receiver reads 18 mA at 80 kPa and 15 V power
supply, the receiver should read 16.8 mA under the same
pressure with 14 V power supply.
For best results it is mandatory to use a regulated power
supply. If that is not possible, the circuit must be modified by
inserting a 12 V regulator to provide a constant supply to the
pressure sensor.
When using a Motorola MC78L12AC voltage regulator, the
circuit can be used with power voltage variation from 14 to
30 volts.
The following results have been achieved using an
MPX2100DP and two MC33078s. The resistors were regular
carbon resistors, but pairs were matched at
±
0.3% and
capacitors were 0.1
μ
F. The load was 150 ohms and the
transmission line was a two pair telephone line with the
+15 Vdc power supply connected on the remote receiver
side.
Note:
Best performances in temperature can be achieved
using metal film resistors. The two potentiometers must be
chosen for high temperatures up to 125
°
C.
The complete circuit with pressure sensor is available
under reference TZA120 and can be ordered as a regular
Motorola product for evaluation.
F
Freescale Semiconductor, Inc.
n
.