AN934

Calculating the calibration for multiple operating temperatures

Doc ID 6393 Rev 4

9/14

Calculating the calibration for multiple operating

temperatures

For applications that spend significant time at more than one temperature, the following

equation may be used to calculate the appropriate amount of calibration required:

where:

acc = Accuracy, in ppm, of the frequency, at the turnover temperature

N = Number of temperature ranges

Consider a piece of portable equipment used outdoors for 8 hours per day, then stored at

room temperature for the remainder of the day. The equation below calculates the

calibration value at –20°C for a period of 8 hours and then room temperature for the rest of

the day for a device that is currently in error by +5 ppm at room temperature:

The unit is losing 1.67 seconds per day (or 50 seconds per month). The appropriate sign bit

in this case is a logical “1,” indicating the clock needs to be sped up to compensate for the

lost time. This yields a calibration value of “100101.”

t

N

Σ

i1

=

–

()

2

×

+

6

–

×

=

8hours

28800

onds

sec

=

16hours

57600

onds

sec

=

28800

s

sec

()

50.036

–

ppm

2

⁄

()

20

°C25°C

–

–

()

2

×

()

+

()

×

[]

57600

s

sec

()

50

+

()

×

[]

+

{

}

=

10

6

–

×

t1.67

–

s

sec

day

⁄

=