I have connected temperature sensor Jumo Dtrans T100 with controller AT39. It shows me digital value from 0= 4mA to 2000=20mA. I don't know how can i calculate temperature in C or F, because i am not familiar with sensors.
temperatures between -50...+260°C

How can i maintain temperature range? For example if i want to measure from 30 C to 100 C.
Pls help me.
best regards
sheikh

 

Sheick

It won't depend on your sensor (as long as you are withing its measuring range) but from your controller range.

Let say you controller (or transmitter if any in between sensor and controller) range from -50 to 260 °C (or°F but this also depend of your controller) then your 4ma will be associated to -50°C (or°F) and your 20ma will be associated to 260°C (or°F), anything in between is linear (assuming your controller is)

i.e: at middle range =12ma you should read a temperature of (260 °C) minus (-50°C) Divide by 2 plus (-50°C) or (310°C/2)+(-50°C) =105°C (this is only mathematics for a straight line calculation y=ax+b.
Now if you want to program you controller with a minimum of 30°C and a maximum or 100°C it is exactly the same story except that of course now your 4ma is associated with 30°C and you 20ma will be associate to 100°C (so middle position or 12ma will read 65°C (as per the same formula)

As you can see it is all in your controller not in the sensor (once again as long as you are within its range measurement) so you need to find a way to "see" what is inside you controller (or transmitter if any) the range (and the scale °C or°F) of its temperature input card whatever the range you want to measure.

Clear?
pascal

 

Hello Pascal,

first of all i want to thank you for ur reply.ur reply has cleared many points. Actually AT39 controller can execute only my program, which is written in C. Controller has nothing to do with range. my sensor has range from -50C to 260C.

please give me more example.

if i want to measure temp from 30C to 80C and my controller shows me 13,5 mA.
i will use this equation y=ax+b.
where a=? x=? and b=?
is it same also with pressure sensor, because its output also 4-20mA or 0-10V?
Do u have any website where i can read about it.

Thank you in Advance
best regards
Sheikh

 

Have a look at

http://www.jumo.ru/upload/iblock/dc4/t90.2815gb.pdf

it is clearly explain that either you use a transmitter and in that case ALL I explain you earlier do apply or you ARE NOT using a transmitter and you are with an single RTD and the range is -50 to 200 °C (260°C,as you mentioned, is only with intermediate tubing and this one is NOT working without transmitter) but it will not work with your controller as in that case it is not a 4-20 ma but only resistance you need to measure and according to what I understand you controller is not able to so.

But if I understand well you should be also able to ask the manufacturer for a special device which can suit YOUR application, so maybe if you talk with them they will provide you with a 4-20ma with YOUR temperature range without transmitter (or at least the transmitter will be part of the sensor) look at following

http://www.jumo.se/sv_SE/press/arkiv/PI_1511.html

So all I said previously DO APPLY you just need to replace word "controller" by "transmitter" (which by the way I also told about) and of course you can select the range you wish for your application but in that case you need the programming device:

Setup program on CD, multilingual part number 90/00485016

and all the accessories which goes with it have a look at their site all is clearly stated there.

So to answer your questions:
Hello Pascal,

first of all i want to thank you for ur reply.ur reply has cleared many points. Actually AT39 controller can execute only my program, which is written in C. Controller has nothing to do with range. my sensor has range from -50C to 260C.

NO your sensor has effectively a range of -50 to 260°C (only with intermediate tubing by the way if not the range is only up to 200°C) but your controller which (if not mistaken from my side) is reading only 4-20ma and the "output" of an RTD is Ohm not ma therefore you need a transmitter to convert Ohm to ma (and in that case the range is the one you program inside your transmitter)

please give me more example.

if i want to measure temp from 30C to 80C and my controller shows me 13,5 mA.
i will use this equation y=ax+b.
where a=? x=? and b=?
Y is your output in ma , X is your input in °C
You already know two points 4 (ma) = 30 (°C) * A + B and 20 (ma) = 80 (°C) * A +B
Solving these equations (I hope you remember this if not I can also explain you this part)
You find A= 0.32 (ma/°C) and B = -5.6 °C and your formula becomes
Y (ma) = 0.32 (ma/°C) * Y(°C) - 5.6°C
We can verify such as 4 = 30*0.32 -5.6 which is true and 20 = 80 *0.32 -5.6 which is also true
Now to answer your example you are looking at which temperature will give you 13.5 ma
You need to "reverse" the formula
13.5 = 0.32 * X (what we are looking for) -5.6 or (13.5 + 5.6 ) / 0.32 = 59.6875 °C (which is slightly above the middle range so is correct too (middle range is 12 ma and if you apply the same formula you also find (12+5.6) / 0.32 = 55 °C and (80-30)/2 +30 = 55 confirm the correctness of the equation.

is it same also with pressure sensor, because its output also 4-20mA or 0-10V?
YES the Principe is exactly the same all those transmitters are designed to be linear (with tolerances) all over their ranges so you can apply the same formula what ever ma or volt and temperature (both is °F or °C ) and pressure (what ever the units)
Do u have any website where i can read about it.

Any mathematical site explaining straight line equation will explain this and regarding transmitters you can try Rosemount (there are other ones of course) site they are good at transmitters you should be able to find something there

Thank you in Advance
best regards
Sheikh

Sorry for this very long answer I hope all is clear now? Pascal

 

HI pascal

ur answer is sum what to the point but i need to add to it that if ur not having a transmitter in between ur sensor and controller then hw could u change the values.

In that case u can just change it from ur controller card on DCS and what happens if ur channel at DCS fails this may trip your plant and u could be in trouble for the same.

If their is a transmitter for the same u can do it by connecting it via HART and changing its range and accordingly u would be having an O/P on SCADA.

I hope so u get to my point?????

Best Regards,
ROHIT JAIN

 

Answer is: "you cannot”"

The sensor is giving you values in ohm and whatever the temperature will be (within its range of reading). No sensor will give you the range you where talking about (30 to 100°C) this will be done by either transmitter or input card of your controller.

If you want to have some "limiting" range and also an input in 4-20 ma you need whatever "converter" you can use Transmitter is one, input card of controller is another as long as you can convert from ohm to 4-20 ma. But in all case you will need a "converter" from ohm to ma and this converter will also be your limiting range device.
Yes you are right if input card fail you may trip your plant but if transmitter fail you may also trip your plant and if sensor fail you may also trip your plant, if the wiring fail can also result in a trip, all depending how is your design and how critical is your temperature reading, not all sensors, transmitters, wiring, etc.. are critical and do trip plants some of them are only for alarm display without trip or even some are only for display not even an alarm nor a trip. On some old plants it is not rare to see unused sensor and transmitter (as they failed and have not being replaced) and the plant is still running without them.

I cannot answer on SCADA as I don’t know! but you are talking HART and what is Hart if not a converter???

pascal

 

I am working with temperature sensor Jumo DT100. I need to know how can u convert mA into temperature and how to make new range of temperature.

4-20mA -> 0 - 2000 -> -50c - +260c: 2000/16=125, so each mA gives u 125.that means for 4mA you will get 0, for 5mA you will get 125...similarly for 20mA you will get 2000.<pre>
mA integer value temperature
4 0 -50
5 125 -30.625
6 250 -11.25
....
....
...
20 2000 +260</pre>