ALL-TEST PRO ATPOL II, User Manual

Page: 55 / 109

55
Measurement Modes
Introducing Measurement Modes
ATPOL II performs so many measurements that it is quite a challenge to keep the instrument easy to
use. Often, you make measurements on one general type of system. There is no need to complicate
your task by ATPOL II asking you to make the same choices over and over. Many of the basic choices
define how you wish ATPOL II to interpret its inputs and how you want it to calculate and record its
results. To accomplish these ends, several measurement modes can be selected by the user. The
general categories are:

Voltage measurement modes

Frequency measurement modes

Power measurement modes

Defining inputs
All measurement modes will be explained in the next few sections.
The [Measure Mode] key allows you to make these basic choices only when needed. As new
measurement capabilities are added to ATPOL II, the [Measure Mode] key will keep the product easy to
use.
Phase-Neutral vs. Phase-Phase vs. 2 Current Mode
There are three voltage measurement modes:

Phase-Phase

Phase-Neutral

2 Current Mode.
When measuring voltages, you either need them recorded in phase-neutral format or in phase-phase
format. A phase-neutral voltage reading is the difference in potential between one of the phase inputs
(V
1
, V
2
, and V
3
) and the neutral input (V
N
). They are presented as V
1N
, V
2N
, and V
3N
. A phase-phase
voltage reading is the difference in potential between two phase inputs. They are presented as V
12
,
V
23
, and V
31
.
Wye systems are usually measured using phase-neutral voltages. Delta systems are usually measured
using phase-phase voltages. On occasion, you may wish to measure phase-phase voltages in a wye
system if the equipment that you are monitoring bridges two hot voltages (like a single- phase air
conditioner running at 240 V).
In a perfectly balanced three-phase system, the phase-neutral voltage is equal to the phase-phase
voltage divided by the square root of 3 (Vpn=Vpp/1.732). In practice, systems are usually not
balanced, but this gives an idea of what voltage to expect as you change the voltage mode from phase-
phase to phase-neutral.
There is a third voltage measurement mode that may be active in your unit. It is the 2 current mode (or
the V
12
,V
32
only mode). In this mode, only two phase-phase voltages are used and displayed. The 2
current mode actually involves a different method of measuring power and therefore is actually a
different power measurement mode, but since it is independent of the other power measurement
modes and yet is an alternative to the other two voltage measurement modes, it is treated as a voltage