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AN272
Application Notes
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Analog Devices AN272 Application Notes

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AN-272
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One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • 781/329-4700 • World Wide Web Site: http://www.analog.com
APPLICATION NOTE
Accuracies of the AD590
The following tables contain maximum errors by grade for applications involving limited temperature spans. The tables reflect the worst case nonlinearities of the AD590, which invariably occur at the ends of the speci­fied temperature range. The “trims” in each table refer to the error correction circuits on pages 4 and 5 of the AD590 data sheet (Figures 4 and 7a). All accuracies given below are ±°C. For example, ±1°C accuracy is
M GRADE
Number Temperature Of Trims Span (8C) –55 –25 0 +25 +50 +75 +100 +125
One 10 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.2 One 25 0.4 0.3 0.2 0.2 0.2 0.2 0.3 0.4 One 50 0.5 0.4 0.3 0.3 0.3 0.4 0.5 — One 100 0.8 0.8 0.7 0.7 0.8 — — — One150 0.90.90.9————— One205 1.0———————
Two10 0.1******0.1 Two25 0.1******0.1 Two50 0.2*****0.2— Two 100 0.2 0.1 * 0.1 0.2 — — — Two150 0.30.20.3————— Two205 0.3———————
*BeIow ±0.05° C
required over the +25°C to +75°C range, then trimming a J grade device using the circuit of Figure 4 on the AD590 data sheet will result in a sensor of the required accu­racy and range.
Lowest Temperature In Span (8C)
AN-272
L GRADE
Lowest Temperature In Span (8C)
Number Temperature Of Trims Span (8C) –55 –25 0 +25 +50 +75 +100 +125
One 10 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.2 One 25 0.5 0.4 0.3 0.3 0.3 0.3 0.4 0.5 One 50 1.0 0.8 0.6 0.6 0.6 0.8 1.0 — One 100 1.3 1.2 1.1 1.1 1.3 — — — One150 1.41.31.4————— One205 1.6———————
Two10 0.1******0.1 Two25 0.1******0.1 Two50 0.2*****0.2— Two 100 0.3 0.2 0.1 0.2 0.3 — — — Two150 0.30.20.3————— Two205 0.4———————
*BeIow ±0.05°C
K GRADE
Lowest Temperature In Span (8C)
Number Temperature Of Trims Span (8C) –55 –25 0 +25 +50 +75 +100 +125
One 10 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.2 One 25 0.6 0.4 0.3 0.3 0.3 0.4 0.5 0.6 One 50 1.2 1.0 0.7 0.7 0.7 1.0 1.2 — One 100 1.5 1.4 1.3 1.3 1.5 — — — One150 1.71.51.7————— One205 2.0———————
Two10 0.1******0.1 Two25 0.20.1****0.10.2 Two 50 0.3 0.1 * * * 0.1 0.2 — Two 100 0.5 0.3 0.2 0.3 0.7 — — — Two150 0.60.50.7————— Two205 0.8———————
*BeIow ±0.05° C
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AN-272
J GRADE
Lowest Temperature In Span (8C)
Number Temperature Of Trims Span (8C) –55 –25 0 +25 +50 +75 +100 +125
One 10 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.3 One 25 0.9 0.6 0.5 0.5 0.5 0.6 0.8 0.9 One 50 1.9 1.5 1.0 1.0 1.0 1.5 1.9 — One 100 2.3 2.2 2.0 2.0 2.3 — — — One150 2.52.42.5————— One205 3.0———————
Two10 0.1******0.1 Two25 0.20.1****0.10.2 Two 50 0.4 0.2 0.1 * * 0.1 0.2 * Two 100 0.7 0.5 0.3 0.7 1.0 — — — Two150 1.00.71.2————— Two205 1.5———————
*BeIow ±0.05°C
I GRADE
Lowest Temperature In Span (8C)
Number Temperature Of Trims Span (8C) –55 –25 0 +25 +50 +75 +100 +125
None 10 8.4 9.2 10.0 10.8 11.6 12.4 13.2 14.4 None 25 10.0 10.4 11.0 11.8 12.0 13.8 15.0 16.0 None 50 13.0 13.0 12.8 13.8 14.6 16.4 18.0 — None 100 15.2 16.0 16.6 17.4 18.8 — — — None 150 18.4 19.0 19.2 ————— None 205 20.0 ———————
One 10 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.6 One 25 1.8 1.2 1.0 1.0 1.0 1.2 1.6 1.8 One 50 3.8 3.0 2.0 2.0 2.0 3.0 3.8 — One 100 4.8 4.5 4.2 4.2 5.0 — — — One150 5.54.85.5————— One205 5.8———————
Two 10 0.3 0.2 0.1 * * 0.1 0.2 0.3 Two 25 0.5 0.3 0.2 * 0.1 0.2 0.3 0.5 Two 50 1.2 0.6 0.4 0.2 0.2 0.3 0.7 — Two 100 1.8 1.4 1.0 2.0 2.5 — — — Two150 2.62.02.8————— Two205 3.0———————
*BeIow ±0.05°C
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AN-272
NOTES
1. All accuracies excluding the 205°C span are guaran­teed, not tested; the 205°C span accuracies are tested for by testing each device at –55°C, +25°C, +125°C and +150°C.
2. All one-trim accuracies excluding the 205°C span as­sume that the trim is made at the midpoint in the span; the 205°C span assumes a trim at +25°C.
3. All two-trim accuracies excluding the 205°C span as­sume that the trims are made at the endpoints of the span; the 205°C span assumes that trims are made at approximately 0°C and +140°C.
4. All accuracies exclude: a. Trim error in calibration technique used; b. Repeatability error; c. Long-term drift errors.
In precision applications, the actual errors encountered are usually dependent upon sources of error that are of­ten overlooked in error budgets.
A)
Trim Error
error arises from such sources as:
1. Poor thermal coupling between the device to be calibrated and the reference sensor;
2. Reference sensor errors;
is usually the largest error source. This
B)
Repeatability Errors
the package. The magnitude of this error is solely a function of the magnitude of the temperature span over which the device is used. For example, thermal shocks between 0°C and 100°C will result in an ex­tremely low hysteresis, for a repeatability error of less than ±0.05°C. When the thermal shocks are wid­ened to –55°C and +150°C, the device will typically exhibit a repeatability of ±0.05°C, with ±0.10°C maximum being guaranteed.
C)
Long-Term Drift Errors
operating temperature and the magnitude of the thermal shocks experienced by the device. Ex­tended use of the device at temperatures above 100°C typically results in a long term drift of ±0.03°C; the guaranteed maximum is ±0.10° C. Oper- ating temperatures below 100°C induce no measur­able drifts in the device. In addition to operating temperature, the severity of the thermal shocks in­curred will determine the absolute stability of the device. For thermal shock spans of less than 100°C, the drift is difficult to measure (< 0.03°C). However, for 200°C spans the device may drift by as much as ±0.10°C after 20 such shocks. If severe, quick shocks are necessary in the application of the device, simu­lated life tests are recommended for a thorough evaluation of the error introduced by such shocks.
arise from a strain hysteresis of
are related to the average
E488a–0–4/98
3. Device to be calibrated is not permitted to ther­mally settle;
4. θ
is radically different for the trim and the
CA
application.
PRINTED IN U.S.A.
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