Ectron 441A, Instructions Manual, Page: 44 / 74

The
CAL
mode can be used as a highly accurate linearity check of the equipment that
follows the Model 441A. First, perform the voltage alignment as described in Section III,
and then step the calibration settings over the range of interest, perhaps from zero to full
scale in 10% increments. This test should produce a system linearity check within an
uncertainty of 0.1% of full scale.
VEHICLE APPLICATIONS
Because the modern automobile generates a great variety of sometimes intense noise signals,
acquiring good data, especially from low-level signals, requires extraordinary measures. Ve-
hicle noise usually involves both electromagnetic and electrostatic signals covering the spec-
trum from subaudio to many megahertz frequencies. Signal and power leads usually require
filtering for both normal-mode and common-mode components ahead of the instrumentation
involved. Leads carrying battery power will be “ contaminated” when exposed to engine-
compartment noise for even a few feet unless appropriate precautions are taken.
ABS signals
2
The following example involves using the Model 441A
to monitor the wheel speed sensor signals of an antilock
brake system (ABS) on a vehicle. These signals, ap-
proximately 10 Hz per mile/hour of speed, are typically
generated by a magnetic pickup producing a sinusoidal
signal used by the ABS system. Therefore, the signal
varies from 0 Hz to 1000 Hz for speeds from zero to
100 mph. The signal amplitude increases with speed
from about 30 mV at 10 mph to 3 V at 100 mph. This
signal would be ideal for the Model 441A except for
the noise, both common mode and normal mode, that
has an amplitude of from 1 V to 3 V p-p. Obviously,
without filtering these signals, the output of the converter
would not be very usable, especially at lower speeds.
Because of noise on the power leads in a vehicle, the
recommended power source is a separate battery. If ve-
hicle battery power is used, it is mandatory that addi-
tional filtering be incorporated in the power leads. The
filter should be located adjacent to the enclosure of the
frequency-to-voltage converters, and it should have
60 dB of attenuation from 10 kHz up to several mega-
hertz. Both plus and common leads should be filtered
with respect to a good chassis ground.
Figure 4-7 shows a recommended wiring diagram of an
Ectron Model E408-6 enclosure with Model 441A fre-
quency-to-voltage converters. Power is from a separate
battery. Adjustment of input filter and sensitivity should
Applications Model 441A
4-14
2
The ABS system used for these tests involved General Motors Pontiac and Buick cars using the ITT/Teves
ABS. Although much of the information given here will apply to other ABS, there may be differences. It is
believed that connecting the Model 441A to the ABS signals will not affect operation of the standard ABS;
however, no guarantee of this can be made. Therefore, operation of the vehicle should be carefully tested after
any installation of this sort. These tests were performed using a Model 441. Using a Model 441A, the results
should be better than those shown because of the action of the input filter and response features of the newer
product.