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4.2.2 Low Voltage Option
This option allows the use of a low voltage ac or dc 24V supply. The specification in Appendix A gives full details.
The polarity of the dc supply connection is not important - it may be connected either way round.
4.2.3 Dual Input Option
This is a cost option, enabled on a channel-by-channel basis by means of entering the relevant password in the
'Feature3 Pass' field in Instrument.Security menu described in Section 6.1.6.
For each enabled channel, a pair of thermocouple, mV or mA inputs can be connected to the instrument. These
inputs are called 'primary' and 'secondary', and are terminated at the analog input terminals (An In1 to An In 4)
as shown in Figure 4, above. The primary inputs 1 to 4 are assigned to channels 1 to 4, as normal. Each
secondary input must be soft wired to a maths channel configured as Operation = 'Copy' if it is to be recorded/
displayed/alarmed etc.
Note: Due to the nature of the input circuit, a large offset may appear for secondary thermocouple
inputs. This offset can be removed only by using the input adjust feature described in Section
6.1.9. Because of this offset, the dual thermocouple input option is not suitable for AMS2750D
applications.
Soft wiring is described in Section 9.
Maths channels are described in Section 6.5.1.
Channel configuration is described in Section 6.4.1.
Input adjust is carried out as described in Section 6.1.9.
4.2.3.1 Sample Rate
For dual input channels, both primary and secondary sample rate is reduced to 4Hz (250ms) from the normal
8Hz (125ms).
4.2.3.2 Sensor Break Detection
Input sensor break detection is not supported for secondary inputs. The internal circuit acts as a 'pull up' on the
secondary input which therefore saturates high in the event of a sensor break.
4.2.3.3 Dual Milliamp Offset Correction
If 'Dual mA' is selected as input type, then an automatic offset correction will be made, according to the shunt
value entered in channel configuration. Refer to Section 6.4.1 for further information.
4.2.3.4 Input Range Limitation
There is no 10V range associated with the secondary input. Any input greater than +2V or less than -2V is
deemed to be 'bad range'.
4.2.4 Modbus Master communications
The master instrument can be connected directly to up to two slaves using standard Ethernet network cable
either directly (single slave only) or via a hub or switch (one or two slaves). In either case, 'straight through' or
'crossover' cable may be used. The cable is terminated at the RJ45 socket at the rear of the unit.
4.2.5 EtherNet/IP
The Client and Server are connected in the same way as described above for Modbus Master communications,
except that there can be only one client and one server.
Page 14
FEC920: USER GUIDE
A5E45696052A Rev-AA
A
September 18
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