Embedded Files
November 2012
In the previous sections we looked at READ only controls; Display, Lamp, Image, Web and Text.
Home Desktop.DASH
In this section we'll look at using the WRITE-able controls, which are SLIDERS for numerical values and BUTTONS for binary values.
Slider Control
The slider control permits the user to send a value constrained by upper and lower limits into the associated PLC store. These stores must be single-word (32767 to -32768) value types only.
From the dashboard menu choose a new Slider control...
New Slider
Select it's Setup properties from the right-click menu...
Slider Properties Not Set
As usual enter a meaningful UserLabel, again without spaces and concise if you want this value accessible via Instant Messenger.
Choose a DataPoint within the target PLC to write the value to.
Important Note
We are using INTEGER values, that's single word (16 Bit) in the range of -32768 to 32767 for FX Series and only 0 to 32767 for an Alpha2.
You may need to apply your own scaling factor as required.
For an example; a heating set-point of 16 to 24 Deg C is probably a little to crude, whereas 16.0 to 24.0 would be ideal.
As we can only read and write Integer values we can apply a scale of 10 to our values, then re-format them in our display, as well as in our controlling PLC.
As an example, we'll enter 160 to 240 in the Min and Max values on the form...
Basic Slider Settings
The slider is one of those controls that can borrow settings from another TAB in the setup form.
So, on the Display TAB we can also select a formatting rule, for example #.#
Using Display TAB's Value Formatting
Finally, press [Ok] to finish...
Slider Scaled
How It Works
Only in "Run Mode" does the slider control have any effect.
Grab the slider and move it. Release it at the desired value indication.
ONLY if the value has changed since you first grabbed the slider will the new value be queued for writing to the PLC.
Desktop.DASH reads all the PLC DataPoints, then it writes any pending values.
Important Notes
SERIAL Device Write Delay. Whilst Ethernet device value writes may react pretty instantly - a fully loaded Dashboard connected to a serial Alpha or FX may not respond for up to 20 or 30 seconds...
In which case, you only need to adjust the value ONCE, then just be patient!
If your PLC program is writing to the same store then your value will be immediately over-written, and the slider will attempt to reflect the value that's actually in the PLC.
Any values sent over the wires into your target PLC should be limited to usable values within the PLC program before they become effective.
Button Control
The button control permits the SET, RESET and PULSE (hold for a duration) of a Binary only value in the target PLC.
You can write to X, M, S and Timer and Counter Coils etc (depending upon the selected driver).
Add a new button from the dashboard menu...
New Button Added
Choose it's setup properties from the right-click menu...
Button Setup For Pulse Mode
How It Works
The PLS function will send a binary 1 to the DataPoint store when you press it. Nothing more will happen until you then release the button, at which point a binary 0 will be sent to the same store.
The SET function will send a binary 1 to the DataPoint immediately as you press the button, releasing the button has no other effect.
The RST function will send a binary 0 to the DataPoint immediately as you press the button, releasing the button has no other effect.
Important Notes
Your PLC program must allow for the event that any value received may NOT be followed up at all in the event of bugs in Desktop.DASH, malfunction in the connection to the PLC or any other conceivable outage along the line. In other words, use these functions very carefully, and consider the impact if any failure could result in excess energy consumption or introduce a hazard in some other way.
For example. If Desktop.DASH has been configured to send a PLS of 1 to such a store that starts a large lighting system, and the PLS release shuts off that lighting, your program in the PLC should also have a timer started such that if the PLS release is not received in a certain time the lights are automatically switched off.
Your PLC program should be self governing in every respect, such that any communications failure does not impede your control from taking action to mitigate negative consequences as a result.
All software based control functions should always sit on top of a hardwired tier of properly devised, safe and compliant to local codes electrical and mechanical systems and should never be relied upon to start and stop machinery or systems "over the wire".
In this section we have completed the fundamentals of using Desktop.DASH. In the next sections we'll look at some of the more fanciful features available.
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