These days as technology has progressed, the cost of telemetry has dropped and the number of options available has grown significantly to a level where today, telemetry for remote downloading of data is almost considered standard.

Campbell Scientific loggers can interface to almost any communications device available, if it has a serial (RS-232 port). This includes most radios, telephone and cell phone modems and cable interfaces. How to interface common telemetry devices to Campbell Scientific loggers is something that many customers have asked us and there are a few things that are critical to getting the connection working.

The first and most significant question to answer is: Does your logger have an RS-232 port?
Our new range of loggers (CR200 series, CR800, CR1000, CR3000 etc), all include an RS-232 port, whereas the older loggers (such as the CR10, CR510 and CR10X) have a CS I/O port only.

RS-232 devices fall into two categories depending on their pin configuration-  DCE and DTE.  A DCE device and a DTE device can be connected together by a straight-through (standard) serial cable.
Devices of the same configuration (DCE-DCE or DTE-DTE) can be connected together by using a crossover (null-modem) cable.

For Example -
A PC normally has a DTE configuration for its serial port.
A modem normally has a DCE configuration for its serial port. These two devices are normally connected together with a standard serial cable.

For loggers with an RS-232 port:
Campbell Scientific loggers (such as CR1000) have a DCE configuration for their RS-232 port, meaning that a standard serial cable can be used to connect the logger to a PC, but a null-modem cable is required to connect the logger to most modems. Always read the manual for your communications device to make sure you know which RS-232 configuration is provided. This will allow the correct choice to be made for cabling between the logger and the communications device.

For loggers with a CS I/O port:
CS I/O is a communications protocol developed by Campbell Scientific Inc to communicate with their early data loggers.  During this time, loggers were programmed with keypads and downloaded using printers as PC’s were not as common as they are today. CS I/O uses different pin configurations and different voltage (logic) levels than RS-232 and it is for these reasons that an interface is required.

There are a number of interfaces available for this purpose and the appropriate product depends on the task that is being undertaken.

• For RS-232 devices with a DTE configuration, such as a PC, the SC32B is the required interface. The SC9 cable can also be used for this purpose.
• For RS-232 devices with a DCE configuration, such as a modem, the SC932A is the required interface. The SC105 interface can also be used for this purpose. The SC105 differs from the SC932A in the fact that it has a range of options that can be set to interface with RS-232 communication devices at different baud rates and with more flexible options. If required, the SC105 will buffer the data as required and send the data to the logger at the logger’s baud rate (usually 9600).
• When using a logger (with a CS I/O port) in complex Pakbus networks, the SC105 is desirable as it can be used in a Pakbus Aware mode, which actually looks at the communications commands and operates appropriately to maximize efficiency.

Important points for interfacing external communications equipment to data loggers:

1. Ensure the logger and the communications device will be communicating using the same protocol (e.g. RS-232) and use the appropriate interface as required.

2. Ensure the logger and the communications device will be communicating at the same baud rate and port settings. The logger or the communications device (or both) may need to have their baud rate setting changed to suit.

3. Ensure the communications device is initialized for incoming connections. This may involve setting commands in the logger program or in the non-volatile memory of the communications device (e.g. Making sure the modem will answer incoming phone calls automatically). For packet data modems, this may include configuring the logger to establish the PPP link with the service provider.

4. Test the communications link as thoroughly as possible prior to installing the system in the field.