Справочник Пользователя для National Instruments DAQ 6527

© National Instruments Corporation

Figure 3-6 shows a signal connection example for both sinking and 
sourcing current. The example shows a TTL-level application with a supply 
voltage of +5 V. The 6527 provides sink current when the relay is closed. 
Resistor R

L

 provides source current when the relay is open.

When the relay is open, little current flows through the resistor and the 
output voltage is close to 5 V, a logic high. When the relay is closed, current 
flows through the load and the output voltage is close to 0 V, a logic low. If 
isolation is not a concern, you can use the +5 V line from the 6527 device 
in place of the external +5 V supply.

Choose a value of R

L

 small enough to provide the source current you need 

but large enough to avoid reducing sink current or consuming unnecessary 
power. For many TTL-level applications, a value of approximately 
R

L

= 5 k

Ω

 works well. This gives a source current at 2.8 V of 

(5 V – 2.8 V)/5 k

Ω

= 440 µA. The sink current at 0.5 V is then at least 

(0.5 V / 35

Ω)

– (5 V – 0.5 V)/5 k

Ω

= 13.4 mA.

Figure 3-6.  Signal Connections for Driving TTL Voltages

The maximum power ratings for the output channels on a 6527 device are 
as follows:

•

Maximum DC voltage across the terminals (V

OUT

) = 60 VDC

•

Maximum AC voltage across the terminals (V

OUT

) = 30 V

RMS

 

(42 V

Peak

)

•

Maximum current (I

f

) = 120 mA

1

1   

With all relays carrying 120 mA and all inputs driven to 28 V, the total power dissipation can approach 20 W. The maximum 

switching capacity in PCI and CompactPCI systems must be derated according to the ambient temperature. (The PXI chassis 
has built-in fans to handle 25 W per slot.)

+5 V

R

L

= 5 k

Ω

V

OUT

Isolation

Isolated
Ground

Digital
Logic

390 

Ω

 

To External +5 V Supply

I

f

35 

Ω

6527