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2.2
Technology
The EL3692 resistance measuring terminal can measure resistances between milliohm (mΩ) and megohm
(MΩ). 2- and 4-wire measurements are supported. The terminal is fully configurable via the Bus Coupler or
the control system. Different output formats may be selected or own scaling activated.
Measuring principle of the terminal
The terminal actively applies a current to the test specimen. This current simultaneously flows through
internal reference resistances. The actual resistance is determined from the proportion of the measured
voltages. The terminal measures ratiometrically, i.e. fluctuations in the supply voltage and/or the measuring
current have no influence on the accuracy.
Fig. 5: Principle of operation
The figure illustrates the following relationship between the known resistance R
resistance R
:
x
R
/ R
= U
/ U
x
ref
x
ref
R
= R
* U
/ U
x
ref
x
ref
The two channels of the EL3692 are measured alternately. To compensate capacitive processes the
conversion time depends on the measuring range: the larger measuring range the longer the conversion. To
measure a resistance at short intervals, the EL3692 should be used in single-channel mode. For measuring
inductive/capacitive loads it should be noted that transition processes influence the result. A delay time can
be specified in the channel settings in the CoE. The measurement and updating of the process data will only
take place once this delay time (in [ms]) has elapsed (CoE 0x80n0:05 and :31 [} 165]). This delay time is
particularly significant in Autorange mode: If it is too small, the measuring range may not change in
Autorange mode because the respective measuring range limits are not reached. The automatic control in
the EL3692 will try to optimize the waiting times, although manual adaptation may still be required.
The measuring frequency is determined from the filter setting for each channel. The lower the filter setting,
the more measurements are carried out and averaged, and the more reliable is therefore the measurement.
The 9 measuring ranges each cover one decade. They each measure from 0 Ohm to 110% of full scale with
their typical measuring current, see table. The measuring ranges of the two channels can be used
independently of each other.
Although all measuring ranges theoretically measure down to 0 Ohm, the relatively large measuring error
and the 2/4-wire connection technology must be taken into account with such small resistances. Apart from
that, it will hardly be possible to achieve a "correct" zero measured value, because not even a connected
(short) wire bridge has a resistance of 0 Ω.
EL3692
Version: 3.1
Product description
and the unknown
ref
17
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