Ph to PLC

[dontknow]

Hi all,

Im working on a project and want to know the best way to connect a PH probe to a Simatic S7-1200 PLC
it can have analog inputs but cant read mA.
so basically i want an probe output like 0 to 5V

thanks in advance

Greetings

 

[keithkyll]

This one from Jenco outputs 4-20 mA.
Wide product range from ASTI. HART or FieldBus communications.

 

[Tom Jenkins]

You can always get a voltage signal out of a current signal by using a dropping resistor acrposs you input terminals. This is a 250 Ohm resistor that will produce 1-5 VDC at 4-20 mA current passing through it. Then you just have to use your programming to accommodate the 20% offset of 1 VDC in the input signal. You loose a little resolution, but the anaolg to digital conversion is going to be an order of magnitude more accurate than your pH probe anyway.

 

[dontknow]

You can always get a voltage signal out of a current signal by using a dropping resistor acrposs you input terminals. This is a 250 Ohm resistor that will produce 1-5 VDC at 4-20 mA current passing through it. Then you just have to use your programming to accommodate the 20% offset of 1 VDC in the input signal. You loose a little resolution, but the anaolg to digital conversion is going to be an order of magnitude more accurate than your pH probe anyway.

Ty for you're reply,
So if i use a 250 ohm resistor i will be able to see the values on the PLC?
only there is one problem.
my probe got a BNC connector. So how am i going to use a resistor and connect it to the PLC when im not permitted to destroy the BNC connector

 

[keithkyll]

You can't read the probe directly with a PLC. You need a signal conditioner to amplify and linearize the signal.
Look at this one from Omega. It has a BNC input.

 

[dontknow]

You can't read the probe directly with a PLC. You need a signal conditioner to amplify and linearize the signal.
Look at this one from Omega. It has a BNC input.

Ty,
can the S7-1200 PLC read a value from 4-20mA?
I dont know how to find out.
or does it need to be converted to 0-5V?

 

[nonuke]

We use a lot of times the S7-1200 but we always configure the analog Input as a 0-10V signal and we use the 499 ohm resistor.
If you buy a PH probe, you will also need the PH transmitter to connect the probe to.
If the transmitter has a 0-10V signal output, you don't need the resistor.

 

[dontknow]

We use a lot of times the S7-1200 but we always configure the analog Input as a 0-10V signal and we use the 499 ohm resistor.
If you buy a PH probe, you will also need the PH transmitter to connect the probe to.
If the transmitter has a 0-10V signal output, you don't need the resistor.

Ty,
do you know some good Ph Transmitters?
im searching atm but i cant find a good PH transmitter.
and what is a regular price for a PH transmitter?

 

[nonuke]

Ty,
do you know some good Ph Transmitters?
im searching atm but i cant find a good PH transmitter.
and what is a regular price for a PH transmitter?

I think you should buy the transmitter from the same brand as the probe. It will be easier with the scales, connections etc.
What is the make and ref. of the probe?

 

[dontknow]

I think you should buy the transmitter from the same brand as the probe. It will be easier with the scales, connections etc.
What is the make and ref. of the probe?

I only know that the probe comes from applikon
and it was made in the USA, hopefully you can find something!

 

[keithkyll]

Probe guess. Contact this company in Germany for help with a selecting a signal conditioner.

 

[dontknow]

Probe guess. Contact this company in Germany for help with a selecting a signal conditioner.

Ty, but no thats not the probe.
It looks exactly like this.
just only the probe.
what do you think is the best interface to buy?

 

[ChrisWOvivo]

Ty, but no thats not the probe.
It looks exactly like this.
just only the probe.
what do you think is the best interface to buy?

Isn't that a process monitoring / sampling instrument?

Usually pH probes are pipe mounted in-line, sometimes under a dome style housing.

How do you mount your probe in the process flow / substance to be measured?

 

[dontknow]

Isn't that a process monitoring / sampling instrument?

Usually pH probes are pipe mounted in-line, sometimes under a dome style housing.

How do you mount your probe in the process flow / substance to be measured?

hmm, i dont get you're question.
i want to connect my probe to a PLC S7-1200
for this i need an interface like thisone.
now i want to know what is the best option, and what is the cheapest interface?

 

[keithkyll]

Manual for probe.
PHTX-014 from Omega Engineering. Do you have an RTD for temperature compensation? Readings will be off if temperature of the liquid changes.
Use a 1000 Ohm RTD.
Link to manual for PHTX-014.
pH reference info from Omega.