OP290_03 Datasheet, PDF (8/12 Pages) Analog Devices – Precision, Low Power, Micropower Dual Operational Amplifier

OP290
From the formulas, it can be seen that if the span trim is adjusted
before the zero trim, the two trims are not interactive, which
greatly simplifies the calibration procedure.
Calibration of the transmitter is simple. First, the slope of the
output current versus temperature is calibrated by adjusting the
span trim, R7. A couple of iterations may be required to be sure
the slope is correct.
Once the span trim has been completed, the zero trim can be made.
Remember that adjusting the offset trim will not affect the gain.
The offset trim can be set at any known temperature by adjusting
R₅ until the output current equals:
( ) ^IOUT
=

∆I _FS
∆T_OPERATING

T_AMBIENT – T_MIN
+ 4 mA
Table I shows the values of R6 required for various tempera-
ture ranges.
Table I.
Temperature Range
0°C to +70°C
–40°C to +85°C
–55°C to +150°C
R6 (k⍀)
10
6.2
3
VARIABLE SLEW RATE FILTER
The circuit shown in Figure 6 can be used to remove pulse noise
from an input signal without limiting the response rate to a genu-
ine signal. The nonlinear filter has use in applications where
the input signal of interest is known to have physical limitations.
An example of this is a transducer output where a change of
temperature or pressure cannot exceed a certain rate due to
physical limitations of the environment. The filter consists of a
comparator which drives an integrator. The comparator com-
pares the input voltage to the output voltage and forces the
integrator output to equal the input voltage. A1 acts as a com-
parator with its output high or low. Diodes D1 and D2 clamp
the voltage across R3 forcing a constant current to flow in or
out of C2. R3, C2, and A2 form an integrator with A2’s output
slewing at a maximum rate of:
Maximum slew rate = ^VD ≈ ^0.6V
R3 C2 R3 C2
For an input voltage slewing at a rate under this maximum slew
rate, the output simply follows the input with A1 operating in its
linear region.
V_IN ²
V_OUT ⁶
REF-43BZ
V_TEMP
3
R1
10k⍀
GND ⁴
2
8
1/2
OP290GP
1
4
SPAN TRIM
V_TEMP R2
1k⍀
R3
100k⍀
R5
5k⍀
R4
20k⍀
R6
3k⍀
R7
5k⍀
6
1/2
OP290GP
7
V_{SET 5}
ZERO
TRIM
R8
1k⍀
R9
100k⍀
1N4002
V+
8V TO 40V
2N1711
R10
100⍀
1%, 1/2W
I_OUT
R_LOAD
Figure 5. Temperature to 4-20 mA Transmitter
–8–
REV. B