Keithley KPCI-PIO32IOA, User Manual

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3-14 Installation KPCI-PIO32IOA and KPCI-PDISO8A User’s Manual
Using +5VDC from the computer power supply
CAUTION Do not connect the +5V DC outputs to an ex5VDC supply.
Doing so may damage the external supply, the board, and the
computer.
The +5V DC output and ground connections are fuse protected and
intended for convenient use in external circuits. This voltage is sup-
plied from the PC bus and is not isolated from the user PC. If isola-
tion is required, do not use this supply to power external circuits, or
use some external means of isolating this supply.
Do not draw more than 1A, total. Drawing excessive current may
damage the KPCI-PIO32IOA or KPCI-PDISO8A board and, poten-
tially, the computer.
The board extends fuse-protected power from the +5V DC computer supply to the I/O connec-
tor(s). This power is convenient for use in light external circuits, such as pull-up resistors. If you
ensure that the conditions in the above
CAUTION
notice are maintained, this power may also
be used to energize external accessories, provided that your computer’s power supply is capable
of delivering the desired current.
I/O considerations
De-bouncing inputs using the low-pass filter
The optional on-card low-pass filter can be used to de-bounce the inputs. A low pass filter for a
given channel can be enabled by installing the appropriate jumper at J100 or J200. See
Figure 3-1 or Figure 3-2 for jumper locations, and the specifications in Appendix A for details
on filter characteristics. Note that use of the low-pass filter is recommended for AC sensing.
Power dissipation limitations
Because of variations in solid-state relay on resistance (3.5
Ω
typical to 4
Ω
maximum), the
actual maximum current may be reduced from the stated 350mA maximum by the maximum
power dissipation limit of 430mW. Current for a given on resistance can be calculated as
follows:
Where: I = current in amps
P = power in watts (430mW maximum)
R = resistance in ohms
For example, with an on resistance of 4
Ω
, the maximum current is reduced to 328mA as follows:
Frequency response limitations
Because optically coupled relays are used for switching, AC signals with higher frequencies may
be significantly attenuated when passing through the board. For that reason, it is recommended
that you use a different board that contains suitable relays if AC performance at higher frequen-
cies is important.
I
P
R
--- =
I
0.43
4
---------- =