i) Planning the correct number of I/O
What will be noticed is if DI, DO, PI, PO, AI, and AO are used to define the signal types the spreadsheet automatically calculates the required number of inputs and outputs per site. Formulae are also in place to help calculate the number of modules required based on the number of required I/O. Although the formulae are based on the Elpro 105U range of modules they are easily modified for any make of telemetry modules. Note how in our example the same type of module is used throughout, this amounts to good system design as only one type of spare is required to maintain the entire system. If just one module in a huge system is different the size of the spares cupboard increases and therefore the costs of the entire system.
This Excel spreadsheet is available for download and may be freely used, modified, and distributed. Handy hints: Inserting more stations should be done by copying the last column across to as many columns as required before filling in any data (if you do copy data across just select the input portion and delete everything copied). Inserting more rows should be done above the "Totals" heading.
If you have spare analogue inputs and/or outputs, and you are prepared to use a little trickery as well, they could very well reduce the number of modules you require and the section "Interfacing Analogue and Digital" is written just for you. This may not be accepted practice among some consultants so do expect some resistance, especially from those who are not electronically adept. At least you have the option open to you.
What will be noticed is the power supply arrangement is displayed too. This is as a result of modules having had some well meaning engineer try to power an instrument from the 24 volt sensor supply which exceeded the 150mA and damaging the module.
| | Ask a Question |15.11.00