Internet PLC Forum
General => Technical support => Topic started by: wrh on May 24, 2005, 07:13:07 PM
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On a T100MD-888+ I need a 0 to 5 voltage ouput on a D/A channel. We have been getting 12V (which is power supply voltage).
We also are tring to input on a A/D channel and it takes reading and adds them by four until it maxes out.
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On the Output why you have 12V i don't really know why but on the input if you don't have anything Connected to the AD input the input values will bounce up to the max Count but if you intall a sensor or if you ground the input it will stay at 0 use a POT so you can check the input with it. here some where they show you the schematic on how to do it too
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Are you sure you are measuring the correct pin? The DA1 and DA2 are on the DB15 connector. You have to measure it with respect to the 0V on the power supply.
Also make sure that your you know which pin is AD1 by looking at the installation guide diagram. A very common error is to mistake AD8 as AD1 and AD7 as AD2.
If you are sure that the DA1 and DA2 are outputting 12V, then something is seriously wrong with the PLC circuit. Please check if the +5V analog reference output is outputing +5V and not +12V.
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I am unsure about what you are referring to as the db15 connector. Currently we are measureing the voltage on the output pins labeled #1 and #2.
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Please refer to the installation guide to find out the exact location of the analog inputs and outputs. It is the D shape looking connector on the left side of the PCB below the RS232 connector.
If you connect to the screw terminal label 1 and 2, these are DIGITAL OUTPUTS and obviously they are power supply voltage when turned OFF.
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Thanks, for the help the controler is working great.
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I'm also using the D/A, and I was wondering if it was possible to get 5V exactly? Whenever I use it, the maximum (when I output 4096) is around 4.8V, and those 0.2 may end up being important down the road. All the other values (when I ouput 2048, etc.) seem to be out of 4.8, as in, if I output 2048, I get 2.4 instead of 2.5.
Thanks
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The maximum value you can get is fullscale - 1 LSB.
So for an 8-bit DAC, the maximum output is 255/256 x 5V
= 4.98V when there is no load. The output are high impedance so you can only connect it to device with high impedance input otherwise the DAC output voltage will start dropping when it draws current.
Did you calibrate the analog output to 5.00V using your volt meter?
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Did you calibrate the analog output to 5.00V using your volt meter?
um, no I didn't? Are you supposed to? And I don't quite know how to do that either...
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There is a CA-AVcc potentiometer on the PCB next to the DB15 connector (for T100MD888+) which you can adjust so that the analog REFERENCE voltage AVcc reaches 5.00V using your multi-meter to measure. . For T100MD1616+ and T100MD2424+ PLCthe +5V analog reference voltage is available on the screw terminal.
For T100MD888+ the analog reference voltage is available at the DB15 connector. However, there is also a solder pad with the marking "AVcc Adj" visible from the top of the PCB which you can probe with the red probe (black probe to 0V) and measure the analog reference voltage. The calibration pot is next to the solder pad.