Datasheet OP290 (Analog Devices) - 10

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OP290 APPLICATIONS INFORMATION TEMPERATURE TO 4 MA TO 20 mA TRANSMITTER
Calibration of the transmitter is simple. First, the slope of the output current vs. temperature is calibrated by adjusting the A simple temperature to 4 mA to 20 mA transmitter is shown in span trim, R7. A couple of iterations may be required to ensure Figure 20. After calibration, the transmitter is accurate to +0.5°C that the slope is correct. over the −50°C to +150°C temperature range. The transmitter operates from 8 V to 40 V with supply rejection better than Once the span trim has been completed, the zero trim can be 3 ppm/V. One half of the OP290 is used to buffer the V made. Remember that adjusting the offset trim does not affect TEMP pin while the other half regulates the output current to satisfy the the gain. The offset trim can be set at any known temperature current summation at its noninverting input. by adjusting R5 until the output current equals V  ∆I  FS TEMP (R6 + R7)  R2 ×R6 ×R7  I = (T −T ) I = −   + OUT A MIN 4 mA   OUT VSET   (1) R2 × R10 ∆T  R2 × R10   OPERATING  The change in output current with temperature is the derivative Table 5 shows the values of R6 that are required for various of the following transfer function: temperature ranges. V ∆
Table 5.
TEMP (R6 + R7 I ∆ ) OUT T ∆ =
Temperature Range R6 (k Ω)
(2) T ∆ R2 × R10 0°C to +70°C 10 −40°C to +85°C 6.2 From Equation 1 and Equation 2, it can be seen that if the span −50°C to +150°C 3 trim is adjusted before the zero trim, the two trims are not interactive, which greatly simplifies the calibration procedure.
1N4002 V+ 8V TO 40V SPAN TRIM R6 3kΩ R4 2 V 20kΩ IN 2 R7 8 5kΩ 6 1/2 V V OUT 1 TEMP 6 OP290GP REF43 R8 R2 3 R1 1/2 1kΩ V 3 7 TEMP 1k 4 Ω 2N1711 OP290GP 10kΩ 4 VSET 5 GND R3 R5 R9 100kΩ 5kΩ ZERO 100kΩ TRIM R10 100Ω 1%, 1/2W IOUT RL
021 00327- Figure 20. Temperature to 4 mA to 20 mA Transmitter Rev. C | Page 10 of 12 Document Outline Features Pin Connections General Description Revision History Specifications Electrical Characteristics Absolute Maximum Ratings ESD Caution Typical Performance Characteristics Theory of Operation Battery-Powered Applications Input Voltage Protection Single-Supply Output Voltage Range Applications Information Temperature to 4 mA to 20 mA Transmitter Variable Slew Rate Filter Low Overhead Voltage Reference Outline Dimensions Ordering Guide