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Reference Manual
00809-0100-4027, Rev AA
December 2005
Rosemount 4500
4-4
Determining Calibration
Frequency
Calibration frequency can vary greatly depending on the application,
performance requirements, and process conditions. Use the following
procedure to determine calibration frequency that meets the needs of your
application.
1. Determine the performance required for your application.
2. Determine the operating conditions.
3. Calculate the Total Probable Error (TPE).
4. Calculate the stability per month.
5. Calculate the calibration frequency.
Sample Calculation
Step 1: Determine the performance required for your application.
Step 2: Determine the operating conditions.
Step 3: Calculate total probable error (TPE).
Step 4: Calculate the stability per month.
Step 5: Calculate calibration frequency.
Required Performance: 0.60% of span
Transmitter: 4500, Range 2 (URL=150 psi),
Calibrated Span: 100 psi
Ambient Temperature Change: ± 50 °F
TPE = = 0.27% of span
Where:
Reference Accuracy = ± 0.15% of span
Ambient Temperature Effect =
ReferenceAccuracy()
2
TemperatureEffect()
2
+
0.2%CS +
0.02% URL
span
--------------------------------
⎝⎠
⎛⎞
per 50 °F 0.23% of span±=±
Cal. Freq.
Req. Performance TPE–()
Stability per Month
----------------------------------------------------------------
0.6% 0.27%–()
0.0042%
--------------------------------------- 78.6 months===
Stability = (% of span for 3 years) = ±0.0042% of span
0.1% URL
span
---------------------------±