Emerson 4500 manual Determining Calibration Frequency, Calculate total probable error TPE

Rosemount 4500

Reference Manual

00809-0100-4027, Rev AA December 2005

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.

Required Performance:0.60% of span

Step 2: Determine the operating conditions.

Transmitter:	4500, Range 2 (URL=150 psi),
Calibrated Span:	100 psi
Ambient Temperature Change:	± 50 °F

Step 3: Calculate total probable error (TPE).

TPE =	( ReferenceAccuracy)2 + (TemperatureEffect)2 = 0.27% of span
Where:
Reference Accuracy =				± 0.15% of span
Ambient Temperature Effect =
	±	⎛	0.2%CS +	0.02% URL ⎞	per 50 °F =	±0.23% of span
		⎝		-------------------------------span ⎠

Step 4: Calculate the stability per month.

Stability = ±	--------------------------0.1% URL	(% of span for 3 years) = ±0.0042% of span
	span

Step 5: Calculate calibration frequency.

Cal. Freq. = (---------------------------------------------------------------Req. Performance – TPE)-	= (--------------------------------------0.6%– 0.27%)- = 78.6 months
Stability per Month	0.0042%

4-4