Sensor read outs

Hi all,

I have two questions. First question is I want read the values from two capacitive proximity sensors to give a read out for example min level and max level. The second question is how do I trigger an alarm when these values are met. I am using siemens step 7 and a s300 plc, to control the level of water in a tank. Is it possible to have the read out initally in the step 7 software and then after display them on the WinCC scada system.

regards

Jimbo

Are you using an analog capacitive sensor or just two discrete capacitive sensors. You would write your logic for the PLC. The scada would then be done.

Regards,
Garry
http://www.accautomation.ca

Hi,

They are capacitive proximity sensors with a 24V binary input.

thank you

Jimbo

SO you will evaluate the input, if low becomes 0 sound alarm.
if high becomes 1 sound alarm.

you can directly add your input addresses in WinCC.

How would I do this in terms of a function block

thank you

Maybe you have to elaborate on your project, or assignment if I assume correctly?

What I understand is that you have 2 digital inputs into a PLC. Say I0.0 and I0.1.

You want an alarm for each of these inputs in a HMI. Then specify these two bits as the alarms. There is no need for any functions of function blocks in the PLC since there is no logic.

Now.. If you want to add some more functionality. Say start/stop filling on these two sensors, in addition to (delayed) alarms, you might want to look at SR (or RS) Flip Flop and On (or Off) Delay Timers (S_ODT/S_OFFDT).

If this is a homework assignment, please be honest and let us know. We might not give you the code, but will help you come to it.

Hi, It is a homework assignment, What I need to do is firstly turn on an alarm at minimum level. Then at a Maximum level turn another alarm on, then with the use of a float switch use that to turn the pump off.

Can this not be done by a function for example, If input(sensor min) is 1 then turn alarm on. If input (sensor max) is 1 then turn alarm on. Or is this not the best way to address the issue

thanks

Sure, that sounds good . I live by the KISS principle. Keep It Simple Stupid .

Just keep in mind, that it is likely your low alarm will come when there is NO water in front of the sensor. The high alarm is opposite. Also, the alarms should have different tasks. Low is likely used to stop a pump (external?) or what ever draining your tank. High alarm should also stop filling in case your float switch fails.

Another thing is that when the level is close to a switch point, the alarm (or pump start/stop) may come and go numerous times. You might want to add a delay to counter this.

Good luck!