Data Sheet

ManualsBrandsRFbeam Microwave ManualsElectronics24GHz digital radar transceiver

Start up time

During start up, the sensor calculates the mean over

the number of FFT frames speciﬁed with the para-

meter start up learn. The start up time of the sensor

depends on this parameter, the sampling frequency

and theFFTsize.

Threshold generation

The calculated mean during start up represents

the noise ﬂoor of the sensor and is stored as spec-

trum average. During operation the spectrum average

is adapted continuously. The speed of this adaption is

conﬁgurable using the parameter threshold noise ad-

aption speed. This mechanism automatically adapts

interferences that are present in both planes ofthe FFT.

This adaptive spectrum average is used together with

the parameter minimum threshold margin to genera-

te the minimum possible threshold level. This means

that the threshold level for each bin cannot be smaller

than the spectrum average + the minimum threshold

margin setting and this is independent of the sensitivity

setting. Adapted interferences are thus automatically

ﬁltered out in the threshold level and do not generate

a detection.

The noise ﬂoor of different sensors can vary. The

sensitivity setting is referenced to the ground line in

order to get an as constant as possible movement de-

tection over different sensors.

The threshold level is deﬁned as an addition of the

parameter minimum threshold offset and the set sen-

sitivity setting for each bin (Further information about

the adjustment of the sensitivity setting can be found

in chapter Adjust Hold Time and Sensitivity).

Startup

= =

Sample

FFT

· N

Value of S05

Sample

256 ∙ N

Value of S05

Figure 8: Minimum threshold level and interference adaption

If the addition of the minimum threshold off-

set and the set sensitivity setting is smaller

than the minimum threshold level (deﬁned

over the spectrum average and the parame-

ter minimum threshold margin), the threshold

is set toitsminimum level.