Texas Instruments 2000 series, Reference Manual

Page: 21 / 52

February 2002 Specifications
21
In order to keep power consumption (P_VSP) below 20 W it is advisable to limit
I_VSP. The maximum allowed value dependent on the configuration can be
determined as follows (in the following examples a supply voltage of 24 V_VSP is
used):
I_VSP =
Where Duty Cycle =
Example 1: Using Standard/Default Settings (
≈
10 read cycles/second):
I_VSP = = 2 A Duty Cycle = = 0.5
Example 2: Configured to No Sync (
≈
12 read cycles/second):
I_VSP = = 1.6 A Duty Cycle = = 0.625
The following methods can be used to measure the actual I_VSP value:
1. Use a battery powered oscilloscope to measure the voltage drop across a
0.1 Ohm resistor placed in the DCIN+ line, and then calculate the actual
current using the formula I = V/R.
2. If a battery powered oscilloscope is not available, measure the potential at both
sides of the 0.1 Ohm resistor (signal probe) with the GND probe at DCIN- and
determine the potential difference.
Ensure that the measured I_VSP value does not exceed the calculated value.
P_VSP
V_VSP x Duty Cycle
Power on time
Total Read Cycle Time
24 W
24V x 0.5
50 ms
100 ms
24 W
24V x 0.625 50 ms
80 ms