CR6 Measurement and Control Datalogger

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1. If a CPI-enabled device is running and there are skipped scans in the data logger, what can be done?

   The default CPI bus speed setting is 250 kB/s. The speed is adjustable in your CRBasic data logger program. Use the CPISpeed() instruction in your CRBasic program to adjust the CPI bus bandwidth to meet the following maximum combined (total) Ethernet cable lengths:

   • 1000 kB/s for maximum combined Ethernet cable lengths of 15.2 m (50.0 ft)
   • 500 kB/s for maximum combined Ethernet cable lengths of 61.0 m (200.0 ft)
   • 250 kB/s for maximum combined Ethernet cable lengths of 152.4 m (500.0 ft)
2. Why are single-ended measurements used in the ACPower() instruction in CRBasic when the outputs of the potential transformer and current transformer are inherently differential?

   The potential transformer and the current transformer provide differential outputs that have galvanic isolation from the voltage and current in the circuit they are measuring. However, there is no need to run the outputs of these transformers into differential inputs of the data logger and unnecessarily consume additional data logger channels. We conducted extensive testing for noise immunity, for inaccuracies from ground loops, and more before concluding that single-ended measurements in the ACPower() instruction have the same performance as differential measurements would provide. Please note that as a result of the galvanic isolation of the potential transformer and current transformer, the data logger ground is NOT connected to the ground of the circuit they are measuring.

   Said differently, you can connect differential outputs of a sensor to single-ended inputs of the data logger. However, doing so creates the possibility of poor common-mode noise rejection in the data logger and the possibility of introducing inaccuracies from ground loops between the sensor and the data logger. Note that in this application, the transformer isolation of the potential transformer and the current transformer eliminates these concerns.

   Simply connect one of the potential transformer secondary wires and one of the current transformer secondary wires to the data logger ground. Which wire in either case makes a difference, as the phase information allows the measurement of power flowing in either direction. If you measure negative real power when it should be positive, then reverse the secondary wires of the potential transformer where they connect to the data logger. Alternatively, you can reverse the secondary wires on the current transformer, but don't reverse both pairs of wires.

3. How does the power usage of the CR1000X compare to the power usage of the CR1000 or CR6?

   When idle, the CR1000, CR6, and CR1000X consume less than 1 mA @ 12Vdc. Similar to the CR6, the CR1000X has a much faster processor that requires more power when up and running. As such, there will be higher current draws during active measurements, serial communications, or when plugged into a PC via USB or Ethernet.

   It may be helpful to think of the CR6 and CR1000X as being built on the same "platform."

4. How many AM16/32B multiplexers can be connected to a data logger at the same time?

   A practical maximum is to connect one multiplexer per every two control terminals on the data logger. Control terminals can be shared between multiplexers to increase the number of connected multiplexers. Sharing terminals, however, requires more complex wiring and programming. Users who would like to connect more than one multiplexer per every two control terminals are advised to contact a sales or support engineer at Campbell Scientific for assistance.