Campbell CR9000, Инструкция по эксплуатации

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Section 1. Installation
1-10
Sensors that have a floating output or are not referenced to ground through a
separate connection may need to have one side of the differential input
connected to ground to ensure the signal remains within the common mode
range.
Problems with exceeding common mode range may be encountered when the
CR9000 is used to read the output of external signal conditioning circuitry if a
good ground connection does not exist between the external circuitry and the
CR9000. When operating where AC power is available, it is not always safe to
assume that a good ground connection exists through the AC wiring. If a
CR9000 is used to measure the output from a laboratory instrument (both
plugged into AC power and referencing ground to outlet ground), it is best to
run a ground wire between the CR9000 and the external circuitry. Even with
this ground connection, the ground potential of the two instruments may not be
at exactly the same level, which is why a differential measurement is desired.
1.5 Use of Digital Control Ports for Switching Relays
The digital control outputs on the 9060 Excitation Module and the I/O
channels on the CR9070/CR9071E Counter Timer Module may be used to
actuate controls but, because of current supply limitations, the output ports are
not used directly to drive a relay coil. Relay driver circuitry is used to switch
current from another source to actually power the relay. These relays may be
used for activating an external power source to run a fan motor or for altering
an external circuit as a means of multiplexing signal lines, etc. CSI's Model
A21REL-12 and A6 REL12 are Relay Controllers using a 12 VDC source for
switching the relays. Solid state relays that may be controlled with a 0-5 V
logic signal are also available for switching AC or DC power.
Figure 1.5-1 is a schematic representation of a typical external coil driven relay
configuration which may be used in conjunction with one of the CR9000s
digital control output ports. The example shows a DC fan motor and 12V
battery in the circuit. This particular configuration has a coil current limitation
of 75mA because of the NPN Medium Power Transistors used (Part No.
2N2222).
FIGURE 1.5-1. Typical Connection for Activating/Powering External
Devices, Using a Digital Control Output Port and Relay Driver