DT80 Range Serial Inputs
From dataTaker Wiki (FAQ)
Does it support SDI-12?
No, the serial sensor port (DT80/85 only) can be configured for RS-232, RS-422 or RS-485 comms standards. The Host port can also be configured as a serial sensor port (RS-232 only).
SDI-12 support is provided by the digital I/O channels. DT80/85: 5D-8D are SDI-12 compatible. DT81/82: 4D is SDI-12 compatible. See section on SDI-12 and user manual.
Does it support Modbus?
1/ Modbus RTU. Yes, the DT80 range loggers includes support for Modbus on all serial ports. The DT80 range loggers are Modbus ‘server’ or ‘slave’ and will respond to requests from a Modbus ‘client’ or ‘master’. If using the RS422/485 the Serial port address can be modified by the MODBUS_SERVER profile settings..
2/ Modbus Master. The DT80 range (from firmware version 8 onwards) can also be configured for Modbus Master where the DT80 is the Modbus master device. This allows connection to Modbus RTU devices such as power meters, PLC's etc. The DT80 is capable of Modbus;
- TCP/IP (Master and slave)
- RS232 (Host port and Serial sensor port)
- RS422 (Serial sensor port only)
- RS485 (Serial sensor port only)
Note: Once configured as a Modbus port, the selected serial channel (Host or serial sensor port) is not available for other use.
How do I program this channel?
String commands and data parsing are programmed using either the DeLogger5 expression builder or in native text code.
Requires knowledge of the data formats and dataTaker command language. Refer to the DT80 range User Manual for additional information.
How big is the serial sensor character buffer?
The buffer is 4096 characters
How many RS485 devices can I connect to the serial sensor input?
The datataker DT80 range meets the RS485 standard which says that up to 32 "unit loads" can be connected. A unit load is defined in the standard. The datataker represents 1/8 of a unit load. Therefore you could connect up to 256 datatakers on the same RS485 network. So the answer to the question depends on the proportion of a unit load of each sensor. If each sensor represent 1 unit load then up to 31 sensors could be connected, remembering that you have to include the datataker as part of the overall load on the network. If each sensor represents 1/8 of a unit load, the same as a datataker, then up to 255 sensors could be connected.
What distance will RS485 work over?
The dataTaker DT80 range meets the RS485 standard which says that distances up to 1200m (4000ft) at speeds of up to 100 kbit/s can be covered. You can use repeaters to cover larger distances. Care should be taken to ensure the the network is properly terminated, especially when the distance covered by the RS485 network is larger.
Can the DT80 wake up on oncoming RS485 data?
To get the DT80 to wake up from sleep mode on incoming RS485 data connect the Tx (Z) terminal to the Rx (A) terminal. You may how ever miss the first couple of characters as the logger wakes from sleep mode.
Why do I get incorrect data or no data on my RS485 connection?
Check that you have set the correct baud rate, using the correct profile setting
Check your wiring.
- Make sure you have a good ground connection between all devices on the RS485 network. If there is a difference in grounds between various devices on the RS485 network then communications can fail. This is more likely when the RS485 network is larger.
- If you are getting no data then you may be connected to the wrong inputs of the serial sensor port. The actual signals on the serial sensor port to connect to are the TxZ and RtsY signals and NOT the RxA and RtsB signals.
- There is often confusion about the correct connection to the "A-" and "B+" inputs of an RS485 devices. Many devices are labeled incorrectly as "A+" and "B-". Try swapping these signals around if you are getting the wrong data. The DT80 range user manual, version UM-0085-A5 and earlier, has an error in the wiring diagram for RS485 that incorrectly shows the TxZ signal connected to the B+ signal and the RtsY signal connected to the A- signal, they should be the other way round as shown in figure 51 on page 189.