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3 - Installation
36
DVM Connections
CAUTION: The DVM may be damaged if voltages at the input terminals exceed ±50 Vdc to ground.
The DVM connector has three pins: plus, minus, and earth ground. The 3-pin connector is removable and
accepts wires sizes from AWG 22 to AWG 14. Disconnect the mating plug by pulling it straight back.
The DVM is designed as an auxiliary measurement input that can measure voltages on circuits that are
powered by the main output (output 1). Voltage measurements can be made on test points inside the
phone under test, or on test points located on the test fixture that is connected to the main output. Figure
3-6 illustrates a common measurement application for the DVM. This example is only provided for
illustration; your specific application will vary depending on the type of test and type of phone.
66319D
66321D
OUTPUT 1
+
−
−−
−
DVM INPUT
lead resistance
lead resistance
Test Fixture
load
current
Minus
terminal
LOAD
+
_
battery
connector
connector for
internal phone
circuits
V common mode
-4Vdc < (V comon mode) < +25Vdc
Figure 3-6. DVM Measurement Example
NOTE: The DVM is not designed to measure voltages that are greater than +25 Vdc or less than
−4.5 Vdc with respect to the negative terminal of the main output. The following sections
discuss restrictions that apply when using the DVM to measure voltages on circuits that are
not powered by the main output, or that are floating with respect to the main output.
Measuring Circuits that are Not Powered by the Main Output
To obtain correct voltage measurements, keep the common mode voltage within the specified limits.
Common mode voltage is defined as the voltage between either DVM input terminal and the negative
terminal of the main output (output 1). The common mode voltage range is from −4.5 Vdc to +25 Vdc.
Attempting to measure voltages outside this range may result in incorrect readings due to clipping by the
internal DVM measurement circuits.
NOTE: Do not confuse the common mode voltage with the DVM voltage readback. The DVM
voltage readback is a differential measurement from one input lead to the other input lead.
This quantity may be as high as ±25 Vdc, depending on the orientation of the input leads.