Idiomas disponibles
Idiomas disponibles
4 Measurement Tutorials
RC protection network
When designing RC protection networks, the protection resistor R
is selected as a compromise between two
p
resistance values. The minimum value of R
is determined by the maximum acceptable relay contact current (I
).
p
max
For the DAQM903A, the maximum allowable relay current (I
) is 1 ADC or AC rms. Thus, the minimum value for R
max
p
is V/I
, where V is the peak value of the supply voltage.
o
The maximum value for R
is usually made equal to the load resistance R
. Therefore, the limits on R
can be stated
p
L
p
as:
Note that the actual value of the current (Io) in a circuit is determined by the equation:
where V is the peak value of the source voltage and R
is the resistance of the load. The value for Io will be used to
L
determine the value of the protection capacitor (C
).
p
In determining the value of the protection network capacitor (C
), there are several things that you will need to
p
consider. First, the total circuit capacitance (C
) must be such that the peak voltage across the open relay contacts
tot
does not exceed 300 Vrms. The equation for determining the minimum allowable circule capacitance is:
where L is the inductance of the load and I
is the current value calculated earlier.
o
The total circuit capacitance (C) is actually made up of the wiring capacitance plus the value of the protection
network capacitor (C
). Therefore, the minimum value for C
should be the value obtained for the total circuit
p
p
capacitance (C). Note that the actual value used for C
should be substantially greater than the value calculated for
p
C.
Keysight DAQ970A/DAQ973A User's Guide
259
