Universal Terminal and Control Port Pairs

Universal terminals can be configured as:

• Analog input channels (single-ended or differential measurements)
• Low level A/C (available on even-numbered terminals only)
• Analog output (current and voltage)
• UART
• High frequency and switch closure pulse counting (3.3 V or 5V)
• Digital I/O

Datalogger terminal functionality is programmed in pairs at program compile time. A terminal pair is two adjacent U terminals or C terminals on the datalogger's wiring panel. Terminal pairs:

• U1/U2
• U3/U4
• U5/U6
• U7/U8
• U9/U10
• U11/U12
• C1/C2
• C3/C4

When a universal terminal pair is programmed for differential measurements, the first terminal in the pair is high and the second is low.

The use of these terminals can be broken down into two functional categories: analog and digital.

Analog Functions (All U Terminals)

• Analog sensor measurements (single-ended or differential, including completion resistors)
• Voltage excitation
• Current excitation
• Vibrating wire (one terminal pair or two terminal pairs, depending upon whether or not thermistor is measured)
• Period Average
• Low-level A/C (even U terminals only)

Digital Functions

• 3.3 V or 5.0 V voltage source (all C and U terminals)
• Pulse count/frequency (all C and U terminals)
• Digital I/O control or status (all C and U terminals)
• RS-232 Recommended Standard 232. A loose standard defining how two computing devices can communicate with each other. The implementation of RS-232 in Campbell Scientific dataloggers to computer communications is quite rigid, but transparent to most users. Features in the datalogger that implement RS-232 communication with smart sensors are flexible. (true R-S232 C1/C2 and C3/C4; TTL all terminal pairs)
• RS-485 Recommended Standard 485. A standard defining how two computing devices can communicate with each other. full and half duplex (C1/C2 and C3/C4)
• RS-422 Communications protocol similar to RS-485. Most RS-422 sensors will work with RS-485 protocol. full and half duplex (C1/C2 and C3/C4)
• SDM Synchronous Device for Measurement. A processor-based peripheral device or sensor that communicates with the datalogger via hardwire over a short distance using a protocol proprietary to Campbell Scientific. control (3 consecutive terminals, Data/Clock/Enable, available on C1, U1, U5, U9)
• SDI-12 Serial Data Interface at 1200 baud. Communication protocol for transferring data between the datalogger and SDI-12 compatible smart sensors. (odd terminals only, C and U terminals)
• Timer I/O (all C and U terminals)
• Pulse width modulation (all C and U terminals)

When the datalogger is programmed, and thus the terminals are assigned their functionality, terminal pairs must match in functionality based upon these two categories. For instance, if a single-ended measurement instruction in the program uses U1, then U2 can be used only for another function in the analog category. Any mismatch in terminal pair assignments results in a compiler error that states the channel is in use.

Note that a differential measurement uses both of the terminals in a pair, with "U-odd" being the high side of the signal and "U-even" being the low side.

Refer to the specification sheet and the datalogger user's manual for additional information.