DL06 Analog Input Problem

shady_yehia

Member
Join Date
Jun 2004
Location
Cairo, Egypt
Posts
30
Hello guys.. I need a little help down here..

I've just taken your advise guys about moving to Automation Direct (koyo) PLC. I bought a DL06 and equiped it with an ethernet module (H0-ECOM) and a 4-in/2-out voltage analog module (F0-4AD2DA-2), what a great thing i've done, isn't it?

i'm using 4 potentiometers to simulate analog signals 0-10 volts as an input to the analog module.

The four potentiometers are supposed to be changing the analog signal from 0 to 10 volts (LINEARLY). the problem is simply that, once I connect the the signals to the analog module, the signal turns to be extramly NON-LINEAR even when the PLC power is off.

i mean with nonlinear that the voltage remains under 1 volt nearly half the scale of the potentiometer, and then starts to rise very fast and reaches 10 volts at the end. But once i disconnect the terminal block from the module and measure again, the signal is back to normal.

Any body knows what is this thing.

Thanks in advance..
 
I think you'll want to add another resistor in series with your potentiometer. Measure the voltage ACROSS this fixed resistor.

The analog module doesn't really provide a current path. If you're measuring voltage, the current into the module will be very small (like an open circuit). In a real-life 0-10V sensor, the current path is all internal to the device. You tap into the circuit where it goes through a fixed resistance.

AK
 
pots

Are you using linear pots or audio pots?

Remove on of the pots and with an ohm meter measure the resistance from one lug to the middle lug. Vary the pot from low end to the high end, checking at precise angles - 0, 1/4 scale, half scale, 3/4 scale and at full scale.

Rod (The CNC dude)
 
First and foremost how are you wiring the potentiometers? The center tap of the pot should be going to the input terminal of the plc with +/- of the voltage going to the 2 outside terminals. Potentiometers are 3 wire devices.

I checked the manual but didnt see a reference to what size pot to use so I would probably use a 1K single turn. The power supply must be a separate 10vdc supply.

There is an update time from event (turn of pot till the plc values change) that may be affected by any programming.

Verify the pots are linear, some arent.

Sometimes you have to use a filter to smooth the analog signal, look at Chapter 7 of the analog module manual.
 
shady_yehia said:
I'm using a 200K ohm pots, would that be a problem?

Maybe, and most likely. Whether or not this is the problem depends on your source voltage. You have to be able to put enough current through the resistor, in order to see a 0 (very small) to 10V differential across the input terminals of the PLC. If your input resistance is much less than 200K, you're going to need a large voltage source.

I think the "rapid" change in response is because your resistance is so large. It would be especially huge if you're using a 1-turn pot. Can you answer a few more questions for us:

1. What's your source voltage?

2. Describe your circuit, or post a circuit diagram.

AK
 
OK akreel, Actually my voltage source is a simple DC power supply (home made), a 220/12 volt Transformer, a bridge, capacitor, a voltage regulator and a potentioneter to fine tune the output voltage.

The Circuit diagram is in the attached file (22.bmp)

Note: the pots are single turn.

please if you have any comments on the circuit, draw it and attach it with your next post.

thanks in advance..
 
Last edited:
Try a 1k or 5K pot. The 220k may be too high a value, this could keep the current down too low until you have turned it half way or more.
 
Module Input impedance

Shady
Yes,the reason is that you are using this high value Pot.taking into consideration that the chaneel input impedance is nearlly 20Kohm according to catalouge so when using this 200K pot you will not reach more then 2.4V on the input even you are midway in your Pot.
try to establish an excel Sheet .do some calculation for the equivelent resistance and current and voltage and you will find what i am talking about.the best value you should use for you pot is 1k this gives you about 4.96V when you are midway in your pot.
Good luck
 
I coudn't find a 1k pot. today, but i found a 85k pot and tried it on. It just proved your theory guys. At the midway to the full scale i hade nearly 3.9 volts at the analog input channel. I will get the 1k pot as soon as i can and let you know.

Thanks for your help.
 

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