Fluke PM-3384B, PM-3380B Trace Point Values, For 16-bit samples Ps = Ts 25600, Trace data

3 - 50 USING THE COMBISCOPE INSTRUMENTS

screen range

	Trace sample value		Trace point
	8-bits	16-bits	value
top - - - - -	100	25600	- 0 dB
- - - - - - -	75	19200	- 10 dB
- - - - - - -	50	12800	- 20 dB
- - - - - - -	25	6400	- 30 dB
mid - - - - -	0	0	- 40 dB
- - - - - - -	- 25	- 6400	- 50 dB
- - - - - - -	- 50	- 12800	- 60 dB
- - - - - - -	- 75	- 19200	- 70 dB
bottom - -	- 100	- 25600	- 80 dB

trace range

Figure 3.19 Relation between screen position and FFT value

TRACE POINT VALUES:

FFT trace sample values, as entered with the TRACe:DATA? query, can be converted to FFT point value as follows:

•Subtract from the sample value the offset value for 4 divisions:

-for 8-bit samples: 4 * 25 = 100

-for 16-bit samples: 4 * 6400 = 25600

•Multiply the result with the following correction factor:

-for 8-bit samples: -10(dB) / -25 = 0.4

-for 16-bit samples: -10(dB) / -6400 = 0.0015625

So, the conversion from a trace sample value (Ts) to a trace point value (Ps) is expressed by the equations:

-for 8-bit samples: Ps = (Ts - 100) * 0.4

-for 16-bit samples: Ps = (Ts - 25600) * 0.0015625

Note:	For an explanation of Ts and Ps, refer to section 3.4.3 "Conversion of
	trace data".

When relative FFT calculation is selected, the amplitude trace point values represent the relative strength of the frequency components. The component with the highest amplitude is taken as the reference level, referred to as the 0 dB level.

When absolute FFT calculation is selected, the amplitude trace point values depend on the absolute reference level as selected via the CURSORS - READOUT front panel menu, which can be one of the following:

-dBm (reference = 1 mW) with REFerence IMPedance of 50Ω

-dBm (reference = 1 mW) with REFerence IMPedance of 600Ω

-dBμV (reference = 1 μV)

-Vrms (reference = RMS signal amplitude)