Hioki DSM-8542, Instruction Manual, Page: 20 / 140

10
3 Operating Principles
3.1 Operating Principles
Equipped with four channels of high-sensitivity current measuring units, this meter
calculates an insulation resistance value based on measuring voltage set in a dedicated
voltage source and impressed to the work and measured current value. The meter also
outputs a current value and can be used also as a 4-channel high-sensitivity ammeter in
addition to its use as an insulation resistance meter.
The control unit of the meter has a 32bit CPU for calculations of resistance values and
for other functions.
Current-voltage conversion of the current measuring unit is based on a current-voltage
conversion A/D converter of a charge measuring type that integrates input current.
The output of the current-voltage converter is converted into digital data by an A/D
converter and is fed to the memory in the control unit after being isolated by a
photoisolator.
The control unit computes measured data input to the memory and outputs it to the
display screen and interfaces.
The measuring voltage source can be set 1000V/10mA maximum and supplies stable
measuring voltage from the dedicated power supply unit.
The dedicated external measuring voltage source of this meter can set a large maximum
output current, allowing simultaneous measurement of up to four channels so that
measuring time can be shortened in measuring a sample with a large electrostatic
capacity such as a capacitor by shortening the charging time.
In addition to voltage output for measurement, the dedicated external measuring voltage
source has voltage output for charging (charging terminal), which can be used for
precharging before taking measurement, to enhance the measuring throughput.
The measuring voltage output and charge output are separated by a current limiter,
enabling continual measurement without affecting measurement even if a sample on the
charge terminal side is short-circuited.
An isolated handler interface that can be connected directly to a contact signal, a GP-IB
interface conforming to the IEEE-488 standard and an RS-232 and an interface for
control of the dedicated voltage source are available as external interfaces that are
supplied as standard provisions.
For measurement connectivity, two channels each measuring circuits are floating. Both
grounded samples and non-grounded samples can be measured.
The meter can be used as an independent ammeter by measuring a current between the
“INPUT” and “GUARD” terminals. In this case, however, measuring voltage is output on
start of measurement and a minimum value needs be set as measuring voltage.