Daisy Chaining - The Basics

Daisy Chaining of instruments allows a user to connect a number of instruments to a single RS 232 serial port using multiple RS 232 cables. This reduces the number of RS 232 serial ports required on a PC. 

When daisy chaining, RS 232 cables are used to connect multiple instruments to together via the computer and network sockets located on the back of most VJ Tech instruments.

Figure 1 - Network and Computer Sockets

When daisy chaining you will need to create a RS 232 (com) port on your PC. VJ Tech would recommend the use of a RS 232 serial port to USB converter such as can be seen in figure 2.

Figure 2 - RS232 Serial port to USB Adaptor

VJ Tech supply high quality RS232 Converters, if you would like to purchase one please contact sales@vjtech.co.uk quoting part number VJT-USB-RS232 to obtain a quote.

Example of Daisy Chaining

Daisy chaining of instruments then follows a simple process, the example below daisy chains four ACONS 2 together:

Figure 3 - Daisy Chaining of four ACONS 2

For For the daisy chain to work with Clisp Studio each instrument daisy chained on a single RS 232 port must have a unique address. The user guide for the instrument provides instructions on how to do this. The user guides are available to download from the VJ Tech website (www.vjtech.co.uk).

In the example above ACONS 1 has an address of 1, ACONS 2 has an address of 2, ACONS 3 has an address of 3 and the final ACONS has an address of 4.

Clisp Studio and Daisy Chaining

Once the instruments have been connected via RS 232 cables and given unique addresses then communications will need to be setup up in Clisp Studio so that the software can control the instrument and read any transducers connected to the instrument.

The following instructions assume:

• Clisp Studio has been installed and a database has been created
• The required instruments have been created in Clisp Studio
• The RS232 to USB converters being used are working

Setting up Communications

• Turn on all instruments in the daisy chain.
• In Clisp Studio open the instrument you wish to setup communications for, normally the first in the daisy chain (the instrument nearest to the computer). In this example the communications for an ACONS is being setup.
• Click on the expander button in the top right hand corner of the instrument window to open the communications setup.

Figure 4 - Instrument window in Clisp Studio

First enter the address of the instrument you are setting up. In this example the ACONS has an address of 1.

Figure 5 - Adding the Unique Address

Next select the correct Comms port from the drop down menu. Comms ports are created by the PC when a RS 232 serial port to USB converter is connected to it. The RS 232 converter as seen is figure 2 would create two Comms ports on a PC.

Figure 6 - Selecting COMMS

Once communications have been established the version box will return the firmware number of the instrument. If communications are not established the version box will remain blank and the COMMS LED will flash.

Figure 7 - Comms LED in Clisp Studio

Note: The COM numbers listed in the Comms Port drop down menu are assigned by your operating system not Clisp Studio. They can be numbered in any sequence. The example above shows a PC with one RS 232 to USB converter (the same as seen in figure 2) connected and the COMMS have been numbered 21 and 22.

For the next instrument in the daisy chain. Open the instrument window in Clisp Studio. Enter its unique address and then select the same COMMS as the first instrument.

Figure 8 - Adding the second instrument in Daisy Chain

Add the addresses and select the correct COMMS for all remaining instruments.

Rules of Daisy Chaining

MPX3000 and MiniScanner 2

An MPX 3000 (VJT3000) must never be daisy chained they must be on their own RS 232 port.

Figure 9 - MPX3000 with RS232 Connection

The network connections on the back of the MPX 3000 are used to connect Junction boxes such as a VJT3000-4D to add additional data logging channels; Other Instruments must not be connected to these ports.

A MiniScanner 2 must also never be daisy chained. It must be connected to its own RS 232 port.

Figure 10 - MiniScanner2 RS232 Connection

The network connection on the back of the MiniScanner 2 is used to connect Junction boxes such as a VJT3000-4D to add additional data logging channels; Other Instruments must not be connected to these ports.

Advanced Instruments

• When using advanced instruments such as Triscan Advanced (these are easily identified as instruments that can have analogue transducers connected to directly to them using a DIN plug) then these cannot be daisy chained together but can be located at the end of a daisy chain with other none advanced instruments.
• An example of how to daisy chain using an Advanced Instrument can be found in figure 11. This is commonly done with an Advanced Triaxial system.

Figure 11 - Correct Daisy Chaining using Advanced Instruments

Instruments such as Sheartest Advanced or Shearscan Advanced cannot be daisy chained as Clisp Studio will not be able to communicate with all the instruments. As these instruments are not normally used with other types of instrument such as automatic pressure controllers, each instrument is usually connected to an individual RS 232 port. A typical setup can be seen figure 13.

Figure 12 - RS 232 Ports on the rear of an instrument labelled Junction Box or CH 5-8 must NOT be used for Daisy Chaining

Figure 12 - RS 232 Connection of Advanced Instruments (no daisy chaining)

Maximum Number of Instruments on a Daisy Chain

The Maximum number of instruments VJ Tech recommends daisy chained to one RS 232 port is 6; more than this and communications between the instruments and Clisp Studio may become unstable.

Additional Help

Additional information or help can be gained by contacting VJ Tech’s support department at service@vjtech.co.uk.

A pdf copy of this blog is available, click here to download.

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