HP 181A manual Typical Versus Worst Case Specifications, Time Interval Measurement LSD Definition

Chapter 7 HP 53131A/132A Specifications

Measurement Definitions (Continued)

Measurement Definitions (Continued)

•Fractional Time Base Error

Time base error is the maximum fractional frequency variation of the time base due to aging or fluctuations in ambient temperature or line voltage:

Time Base Error =	⎛ Δf		Δf		Δf	⎞
	----		+ ----		+ ----
	⎝ f	aging rate	f	temperature	f	line voltage⎠

Multiply this quantity by the measurement result to yield the absolute error for that measurement. Averaging measurements will not reduce (fractional) time base error. The HP 53131A/132A universal counters exhibit negligible sensitivity to line voltage; consequently this term may be ignored.

•Differential Channel Error

The Differential Channel Error term included in many of the Systematic Uncertainty equations accounts for channel-to-channel mismatch and internal noise. This error can be substantially reduced by performing the TI Calibration in the temperature environment in which future measurements are to be made and by careful measurement technique. Calibration is accessible via the Calibration Menu during power-up.

Typical Versus Worst Case Specifications

Specifications identified as “Typical” represent performance of the instrument that the majority of users will perceive under a wide variety of conditions and signals. The specifications identified as “Worst Case” should be used when the instrument is under extreme environmental conditions or when the accuracy of the measurement results are critically important.

Time Interval Measurement LSD Definition

For the Time Interval, Pulse Width, and Rise/Fall Time measurements, the LSD is the measurement quantization error. “ tres” is the LSD plus the effects of certain internal error producing sources.

Additional Considerations for Digits and Time Arming Modes

For sample rates defined below, resolution will be reduced by up to 1 decade. The instruments display detects this condition and displays a reduced-resolution result. Resolution is reduced in a band about fs, such that

7

10MHz x.y = ------------------

fs

where x is any integer, and y is any fraction in the set:

⎧		⁄3,	1 ⁄4 , 2 ⁄4,	3	⁄4,	1 ⁄5, 2 ⁄5,	3 ⁄5, 4 ⁄5 , ...	⎫
⎨0, 1 ⁄2, 1 ⁄3, 2								⎬
⎩								⎭
The width of the band is at most:
±	6 × 10– 7 × finput
	------Gate---------------Time-----------------

For Example:

10MHz

25.25 = ---------------------------

396, 039.6

x = 25

y = 0.25 = 1⁄4

The value of fs is not available to the user, but the instrument can be queried over HP-IB to determine if this condition exists.

After the measurement completes, use the query :DIAGnostic:MEASure:PRESolution? The response is an ASCII text formatted string “Ø” for normal resolution and “1” for reduced resolution. This command is valid only when making frequency measurements in time or digits arming and the input frequency is greater than 100 Hz.

Assembly-Level Service Guide 7-13