Hardware
English, Revision 03, Date: 20.11.2015
10
4
Hardware
The casing of the interpreter is made of plastic. All wires etc. can be connected via
M12 connectors on the front panel. The input signals (two per antenna) are amplified,
filtered with an adjustable band filter (frequency input, see Figure 13 on page 42) and
rectified synchronously. Afterwards the direct current is smoothened by a low-pass fil-
ter (see block diagram, Figure 11 on page 41)
4.1
Monitoring
The function of the antennas is controlled: the horizontal component of the field (sum
antenna) is usually controlled by the threshold bits in the system status as a reference.
The vertical component of the field (difference antenna) equals 0 above the middle of
the wire, but a defective difference channel would always cause a deviation of 0. That
is why both channels are controlled by a DC monitoring. In front of the receiving induc-
tors, 5V are fed into the circuit, which are passed on from amplifier to amplifier until
reaching the interpreter. If this voltage is applied, the status bits DC1-OK respectively
DC2-OK are set.
4.2
Presettings
To run the interpreter under different conditions without having to change the circuit
board, the input signals have been scaled: An input amplitude of 1 V
pp
reaches a full
range of 75 % between sum channel and the difference channel. The Node-ID is pre-
set to 1. The maximal incoming signal of all data streams having other frequencies is
5 V
pp
.
As the parameters of the device (reading height, wire current) can be altered, it is no
problem that the antennas are having different dimensions or being adjusted different-
ly.
The interpreter is preset to a frequency of 10 kHz. The threshold for the calculation of
the distances referring itself to 1000 units is preset on input voltage S1 respectively S2.
If the sum voltage lies above this value, the corresponding bit is set in the system sta-
tus and the corresponding LED CDx lights up. These presettings can be modified us-
ing a serial terminal (for example HyperTerm on a PC) or via the various SDOs of the
CANopen® protocol (s. Table 20 on page 27).
The two channels of the interpreter have the same presettings.
4.3
Processing the signal
The four voltages of the four channels are checked every 500
μ
s and are summed up
during a period of 8 ms. Each 10 ms the CANopen® resp. Profibus protocol are pro-
vided with the measured values. The scaled distances are put out in mms. To calculate
those distances the quotients are formed (current compensated).
The 16x oversampling and the use of a 10bit A/D converter lead to a value range of
the sum voltage of 16384, of the difference voltage of ±8192.
