Current Limiter - Omron K7GE-MG User Manual

4-5

Current Limiter

This function is used to limit the current flowing through a path to a fixed value (under 3 mA) when
applying a Megger voltage.
Due to the flow of overcurrent in the measurement path, the load and the peripheral equipment, as well
as the internal circuit of the K7GE-MG may be damaged. Therefore, the overcurrent is limited with the
current limiter function. The current limiter of the K7GE-MG is composed of analog components having
few delay elements. Therefore, the response speed is extremely fast (μ-second order), and the
overcurrent can be instantly suppressed.
Next, the cases when the current limiter
activates are described.
In the normal state, the measurement
current returns to the measurement
circuit of the K7GE-MG via the
insulation resistance of the load.
Since the Megger voltage of the
K7GE-MG is 50 VDC and the lower limit
value of the measuring range is 0.1 MΩ,
the maximum value of the measurement
current is 50 V ÷ 0.1 MΩ = 0.5 mA.
Therefore, the current limiter does not activate if measurement can be performed normally.
The current limiter activates in the following three types of cases.
 When the Insulation
Resistance is Extremely Low
When the contactor turns OFF, the
load and power line properly turn OFF
and the measurement current also
passes through the insulation
resistance, but the insulation
resistance itself is extremely low. For
example, when the motor coil is in a
metallic case and a short-circuit state.
Insulation Resistance Monitoring Device User's Manual (N224)
4 Functions Related to Measurement
MC
Note The above diagram shows only the parts of the internal circuit of the
K7GE-MG that are necessary for explanation.
MC
Rz → 0 MΩ
Note The above diagram shows only the parts of the internal circuit of the
K7GE-MG that are necessary for explanation.
K7GE-MG
L2
Voltage
Mi c rocomputer
L3
monitoring
Current
Rz
limiter
Megger voltage
(50 VDC)
PE
K7GE-MG
L2
Voltage
Mi c rocomputer
L3
monitoring
Current
Rz
limiter
Megger voltage
PE (50 VDC)
4 - 23
4