What is the Maximum Input Voltage of the 6527 Board?

Hardware: Digital I/O (DIO)>>Isolated>>PCI-6527

Problem: The 6527 User Manual states that the maximum input voltage for the 6527 is 28 V. I am worried that my signal may occasionally exceed 28V. What can I do? Can I input a voltage that is higher than the rated maximum input voltage of the 6527 device?

Solution: The 6527 has a 3k Ohms current limiting resistor that is rated for 0.25W (see image below). The calculation to determine the maximum voltage drop across the resistor is shown below, based on the power rating of the resistor.

Calculation:

V * I = P
V^2 / R = P
V^2 = P * R
V = sqrt (P * R)
V = sqrt (0.25 * 3000)
V = 27.3

The maximum voltage of the circuit is based on the drop across the resistor and the diode. Assuming that the voltage drop across the diode is 0.7V and the maximum voltage drop across the resistor in 27.3V (from above):

Calculation:

V(total) = V(1) + V(2)
V(total) = 27.3 + 0.7
V(total) = 28

Thus, if the voltage goes above 28 V, the current limiting resistor may be damaged. The best way to avoid this is to add an external resistor in series. It will further limit the current going into the 6527.

You can add as much resistance in series as you need to input the higher voltage. Use this equations to determine what size resistor you will need.

Resistance (Ohms) = [(Max Voltage - 0.7)^2 / 0.25] - 3000

Here is a table of some maximum voltages and the minimum resistance to add in series. NOTE: All resistances listed must have a power rating of at least 0.25W.

Maximum Voltage (V)	Minimum Resistance to Add in Series (ohm)
29	204
30	434
31	672
32	919
33	1173
34	1436
35	1706
36	1984
37	2271
38	2565
39	2868
40	3178

Related Links: Product Manuals: 6527 User Manual (August 2000)

Attachments:

Report Date: 09/24/2002
Last Updated: 07/24/2003
Document ID: 2PNFQREV

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