Measuring Mode - Beckhoff EL3692 Manual

Calibration in 2-wire mode
For the lower 3 measuring ranges (10mΩ - 10 Ω) 2-wire mode only makes sense if the connection
characteristics (line lengths, contact resistances) are known exactly. In these 3 measuring ranges
the EL3692 is therefore not calibrated by the manufacturer for 2-wire measurement mode.
In Autorange mode with 2-wire connection these 3 measuring ranges are therefore not used.
The 3 measuring ranges can be used through manual settings (CoE or control word). Previous user
calibration by the customer is essential.
The default state of the EL3692 is 4-wire mode. In this mode the measuring current flows via terminal points
1(5) through the resistance to terminal point 3(7). The voltage measurement takes place via terminal points
2(6) and 4(8).
5.6.6

Measuring mode

The terminal supports 4 measuring modes. The measuring mode is selected via the Mode entries in the
process data (control word) or in CoE 0x80n0:0D [} 166]. The measuring mode determines the time of the
measurement and the wire connection.
• 0: 4-wire measurement
• 1: 4-wire measurement (single-shot mode)
• 2: 2-wire measurement
• 3: 2-wire measurement (single-shot mode)
Measurements
Measurements cannot take place simultaneously on both channels. 4-wire connection is
recommended for the EL3692.
Operating mode Mode entry
Alternating mode Both channels measuring mode "0" or "2"
Single shot mode Both channels measuring mode "1" or "3"
Mixed mode One channel measuring mode "0" or "2", the other
channel mode "1" or "3"
Table 1: Operating modes
Alternating mode
This mode is the delivery state of the terminal. Both channels alternately measure a resistance at their
connection points. The measurement is indicated by the lit status LED.
Single shot mode
Each channel only measures on request by the application. A rising edge in the "Start Conversion" bit in the
control word triggers a measurement. If both channels are triggered simultaneously, the channels are
processed sequentially. The first channel has priority.
This mode is suitable for measurements during which heating of the test specimen due to repeated
measurements is undesirable.
EL3692 Version: 3.1
Commissioning
Principle of operation
145