The ADM2400 volt meter provides AC and DC voltage measurements for line1 and line2. It also provides DC voltage measurements for line3.

Refer to the connection diagram or the ADM2400 User's Guide for more connection information.

The volt meter can be used to test directly at the wall plate or just remove the line from a modem, POS terminal, or other device and connect it to the ADM2400.

Select the VOLT METER tab in AALogic ViewLE, then select the correct line to test. The example shows an idle line (-47Vdcd) with low noise (< .75Vp-p) on line 1.

AC and DC measurements are made and displayed at the same time. AC measurements are displayed as Vp-p or dBm.

This example is a line in use and the modems are communicating.

DC voltages for phone lines are typically negative. The voltage is usually near -48Vdc when idle (not in use) and decreases when the line is in use.

The example also shows AC voltage that is maximum or may exceed the ±1.5Vp-p scale. A maximum scale reading is common when measuring lines while modems are communicating.

You can change lines at anytime and you may have more than one line connected to the ADM2400 at the same time.

CAUTION: Ensure that only one line is connected to lines 1 and 2 before starting the capture mode.

The AC voltage can also be expressed in decibels (dBm). This measurement is useful in measuring noise and is capable of measuring small voltages.

This example is a line with dialtone. The DC voltage is -10Vdc and the AC voltage is approximately -10dBm.

The best way to measure line noise is to connect the ADM2400 directly to an idle line. Large noise readings should be addressed to improve communications on the line.

Note: The reference impedance for dBm readings is 600 ohms.