How to read data from a sensor

There are many different types of sensors available from various manufacturers which will convert physical characteristics such as temperature, pressure, strain, frequency, RPM, etc. into an electrical signal which can be measured by a data acquisition system. Depending on the particular sensor being used, refer to the product data sheets to determine which of the DAQ Modules is appropriate for the task and how to wire it up.

With ModCom, it is a very simple task to set up custom Data Windows to view the data returned from these modules. Simply choose a Data Window from the <Place Object> menu at the top of the screen and move it to the desired position with the mouse. Follow the steps below to set up the object for data collection.

Step 1: To set the properties of the Data Window, right-click on the object. This will bring up the Properties dialog box which contains a number of user defined attributes which can be used to customize the Data Window's appearance and operation.

Step 2: From the command set shown in Table 2 of the product data sheet, choose the command string which is required to retrieve the desired data from the DAQ Module and type it into the "Data Polling Command" space at the upper right hand corner of the Properties dialog box. That's all there is to it!

Step 3: Close out the dialog box and start the main run-time loop by clicking on the green "Run" button at the top of the screen.

Once in run mode, ModCom will automatically poll the DAQ Module and show its return data on the screen in real time. You can place as many Data Windows on the screen that you want. ModCom will take care of all communications and will interleave the transmissions in a way that will maximize the efficiency of the data bus and avoid collisions.

Illegal Command Strings:

If the command string entered into the Properties dialog box is typed in incorrectly, or for any other reason does not return any data from a DAQ Module, the communications routine for that Data Window will time out after a couple seconds, and the "Error" message will be displayed. If this occurs, stop the run-time loop by clicking on the red "Halt" button at the top of the screen and go back and edit the command string in the Properties dialog box. If you are having any trouble understanding the syntax of the DAQ Module's command set, use the Send/Receive dialog box in the <Communicate> menu to test out your command strings ahead of time.

Multiple Screen Pages:

You can create multiple pages in ModCom which contain their own unique collection of Data Windows. These Data Windows will collect data even if their page is not the one currently being viewed. Thereby allowing them to operate in the background sending data to a log file or being evaluated in a Conditional statement for alarm purposes. Use the page-up and page-down keys to switch between pages.

Instrument Gauges:

ModCom provides a number of virtual instrument gauges such as a Level Gauge, a Dial Gauge and a Meter Gauge. All of these are similar to a Data Window except that the data is represented by a graphical virtual instrument instead of a simple number value on the screen. You can use these objects in the same manner as the Data Window described above.