at the transducer. Thus the XTR101 is, in general, very
suitable for individualized and special purpose applications.
20
15
10
Span Adjust
EXAMPLE 1
RTD Transducer shown in Figure 9.
Given a process with temperature limits of +25°C and
+150°C, configure the XTR101 to measure the temperature
with a platinum RTD which produces 100Ω at 0°C and
200Ω at +266°C (obtained from standard RTD tables).
Transmit 4mA for +25°C and 20mA for +150°C.
Elevated
Zero
Range
Suppressed
Zero
Range
5
0
COMPUTING RS:
– 0 +
eIN (V)
The sensitivity of the RTD is ∆R/∆T = 100Ω/266°C. When
excited with a 1mA current source for a 25°C to 150°C range
(i.e., 125°C span), the span of eIN is 1mA X (100Ω/266°C)
X 125°C = 47mV = ∆eIN.
FIGURE 7. Elevation and Suppression Graph.
40
From equation 1, RS =
∆IO/∆eIN – 0.016Ω
1mA
1mA
–
+
1mA
1mA
–
+
eIN
eIN
40
40
RS =
=
Ω
= 123.3Ω
16mA/47mV – 0.016
0.3244
+
+
e'2
+
–
RT
V4
R4
e'2
Span adjustment (calibration) is accomplished by trimming
RS.
–
RT
+
–
–
V4
R4
COMPUTING R4:
At +25°C, e'2 = 1mA (RT + ∆RT)
100Ω
2mA
2mA
e
V
IN = (e'2 –V4)
4 = 1mA X R4
e'2 = 1mA X RT
eIN = (e'2 +V4)
4 = 1mA X R4
e'2 = 1mA X RT
V
= 1mA [100Ω +
X 25°C]
266°C
(a) Elevated Zero Range
(b) Suppressed Zero Range
= 1mA (109.4Ω) = 109.4mV
In order to make the lower range limit of 25°C correspond
to the output lower range limit of 4mA, the input circuitry
shown in Figure 9 is used.
2mA
2mA
–
–
+
eIN
eIN
+
e'2
+
–
eIN, the XTR101 differential input, is made 0 at 25°C or
+
V4
e'2 25°C – V4 = 0
R4
+
+
–
V4
R4
e'2
–
thus, V4 = e'2 25°C = 109.4mV
–
V4
109.4mV
1mA
R4 =
=
= 109.4Ω
2mA
2mA
1mA
e
IN = (e'2 –V4)
e
IN = (e'2 +V4)
V4 = 2mA X R4
V4 = 2mA X R4
COMPUTING R2 AND CHECKING CMV:
At +25°C, e'2 = 109.4mV
At +150°C, e'2 = 1mA (RT + ∆RT)
100Ω
(c) Elevated Zero Range
(d) Suppressed Zero Range
FIGURE 8. Elevation and Suppression Circuits.
APPLICATION INFORMATION
= 1mA [100Ω +(
X 150°C)]
266°C
The small size, low offset voltage and drift, excellent linear-
ity, and internal precision current sources, make the XTR101
ideal for a variety of two-wire transmitter applications. It can
be used by OEMs producing different types of transducer
transmitter modules and by data acquisition systems manu-
facturers who gather transducer data. Current mode trans-
mission greatly reduces noise interference. The two-wire
nature of the device allows economical signal conditioning
= 156.4mV
Since both e'2 and V4 are small relative to the desired 5V
common-mode voltage, they may be ignored in computing
R2 as long as the CMV is met.
R2 = 5V/2mA = 2.5kΩ
e2 min = 5V + 0.1094V
The +4V to +6V CMV
e2 max = 5V + 0.1564V
requirement is met.
e1 = 5V + 0.1094V
®
9
XTR101
BB [ BURR-BROWN CORPORATION ]
