3550 Battery HiTESTER Series
26
Fig. 3: Synchronous detection circuit
The synchronous detection method used with this measuring equipment is the detection method
to determine the signal level of the in-phase components of a given signal and a reference
signal.
Fig. 3 shows a simple example of the
circuit configuration of a synchronous
detection circuit. This circuit consists
of a multiplier, which multiplies together
the two signals, and an LPF that
removes just the DC component of the
output from the multiplier. Assuming "
v
1" as the voltage of the reference signal for the constant
alternating current generated by the measuring equipment, and "
v
2"as the voltage of the signal
in which synchronous detection is to be performed, these values can be expressed by the
following equations:
v
1 =
Asin
ω
t
……..……(1)
v
2 =
Bsin
(ω
t
+ θ)……(2)
where A and B are the amplitudes of "
v
1" and"
v
2" , respectively, and θ in equation (2) is the
phase difference from "
v
1" due to reactance. If synchronous detection as shown in Fig. 3 is
performed using "
v
1" and "
v
2", the result can be expressed by the following equation:
v
1 x
v
2
= ABsin
ω
t sin(
ω
t
+ θ
)
=
1/2
ABcos
θ - 1/2
ABcos(
2ω
t
+ θ
)
………(3)
Fig. 2: Configuration of Internal Resistance Measuring Equipment
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