Chapter 4: Instrument Calibration

1
Chapter 4 Instrument Calibration

• Agenda
• Process instrument calibration
• Working Standards
• Standard laboratories
• Primary reference standards
• Calibration Procedures

2
Process Instrument Calibration

• Instrument calibration the outputs of tested
  instrument standard one
• Calibrate in process ?
• Instrument calibration chain
• Instruments characteristics changes over a period
  of ? Working standards experience

3
Process Instrument Calibration

• For longer term, working standards will
  .? calibrate working standard by authorized
  standards laboratory (secondary reference
  standard).
• Primary reference standards describe the level
  of accuracy that is achievable in the
  measurement of any particular physical quantity
• The standard instrument must be kept for
  in the calibration area with environmental
  control high-accuracy, null-type device

4
Process Instrument Calibration
5
Calibration Procedures

• Determine
• Quantify the parameter, that differ from the
  , on the output
• the investigated parameter over a range of
  values ? output
• Draw the
• Apply the inputs of varying magnitude to the
  the instrument

6
Determination of the Calibration Frequency

• Apply the following checking frequency of
  instrument characteristics (Assume 24 working
  hours/day)
• Day 1 once/h for the first 4 hours, then every
  4h
• Days 2-3 every 12h
• Days 4-7 once per day
• Weeks 2-3 twice per week
• Weeks 3-4 Once per week
• Week 6 once
• Week 8 once
• Months 3-6 once per month
• Month 9once
• Month 12 once
• Month 18 once
• Month 24once
• Then once per year
• If at time t the deterioration in accuracy is
  close to the permissible limit ? calibration
  frequency

7
Example

• A company ABC produces a certain type of IC. The
  quality control department checks the output
  current of the ICs before it is sended out to the
  customer. The dependence of the out current of
  ICs with the environmental temperature is as
  follows
• I 1 0.01T (1)
• To check the time to recalibrate the Ampere
  meter, the QC staff perform the following
  checking scheme and the measurement results is
  given in the following table
• Checking T(oC) 25 25.1 25.2 25.3 25.4
  25.5 25.6 25.7 25.8 25.9
• Time
• Shift1day1 I(mA) 1.3 1.25 1.28 1.32 1.27
  1.22 1.18 1.29 1.23 1.35
• Shift2day1 1.25 1.34 1.30 1.28
  1.32 1.27 1.31 - 1.33 -
• Shift3day1 - 1.24 1.31 1.26
  1.33 1.35 - 1.23 1.25
• Day5 1.33 1.20 1.26 1.45
  - 1.23 - - 1.45 -
• Week 2 - 1.24 1.33
  1.45 1.56 1.45 1.20 1.37 1.42 1.26
• Week 3 1.34 1.25 1.56 1.37
  1.28 1.22 - 1.35 1.32 -
• Month 2 - - 1.20
  - 1.36 1.31 1.23 1.18 - 1.34
• Year 1 1.15 1.16 1.33
  - - 1.42 1.41 1.33 1.26 1.44
• If the acceptable error of measurement device is
  8. What is the recalibration frequency?

8
Solution

• From equation 1, we substitute the value of
  checking time (T )
• T(oC) 25 25.1 25.2 25.3 25.4 25.5
  25.6 25.7 25.8 25.9
• I (mA) 1.25 1.251 1.252 1.253 1.254 1.255 1.256
  1.257 1.258 1.259
• Therefore, the errors are e (measured I
  I)100/I
• If e gt 8 we recalibrate
• Checking Time Average error
• Shift1day1 (0.04810-40.072) / 10 0.033
• Shift2day1 ( 0 0.0710.057) / 8
  0.036
• Shift3day1 (0.0090.0460.006)/7
  0.033
• Day5 (0.0640.0410.153)/6 0.051
• Week2 (0.0090.062810-4)/9 0.099
• Week3 (0.072810-4 0.049)/8 0.073
• Month2 (0.0420.0850.064)/ 6 0.052
• Year1 (0.080.0730.144)/8
  0.083
• We should recalibrate every 2 weeks.