Actuators

I've been reading the Shimaden SR-73 manual and it says that terminals 1, 2, and 4 are communications terminals. You need to be using terminals 13, 14, and 15 which are the controller output terminals (free contacts).

You didn't give the model for your Industrie Technik actuator so I can't tell if you've got it correctly connected or even if it's suitable for this application.

What kind of control are you using? Do you just open and close the valve (no intermediate position)?

I'm asking because, the SR-73 doesn't seem to have the ability for three-point-control (open-stop-close). The valve is either fully open or fully closed. It controls temperature by changing the time that the valve is open. If your output is at, say, 50%, the valve is open 50% of the time and closed 50% of the time.

Thanks for the reply. Sorry but I made a mistake on the posting. I'm using 13, 14 and 15 it's just that they've been connected to a rail marked 1,2 and 4. Stupid mistake I just wasn't thinking.

As for a model number all I can see is DM1.1

The chiller came as a pre-assembled unit from greece and there seems to be no info on this particular actuator. Basically this actuator is controlling a 3 way valve on the evaporator side of the chiller. The 3 way valve controls the quantity of water circulating through the heat exchanger (to chill seawater). In other words the water is passing the evaporator and being cooled or being diverted through the heat exchanger.

What you say about the SR-73 not being three-point-control makes sense. I couldn't figure out how the valve knows when to stop in an intermediate position because the output from the SR-73 will only make the motor spin one way or the other but I have actually witnessed the valve stopping in an intermediate position in the past. This may however been the start of a fault which has now shown itself.

You're not the only one making mistakes. I had another look at the manual and the actual output is terminals 14, 15, and 16. I probably need new glasses.

Another thing I overlooked, the manual says that these output terminals could also provide a voltage or current signal. Check the complete model number on your unit to find out if this is what you have. If so, your actuator should position itself depending on the value of the output.

Check the parameters inputted into the unit. Quite possibly (and I've seen this happen), the P (proportional) or I (integral) values my have been set improperly. Too high a gain and the unit gives a huge output in response to the error. The same thing can happen with a very fast integral setting.

Just realise in original posting I also said it was the cooling water throught the condenser. That should have been evaporator.

Got a stinker of a cold and my brain function seems a bit low at the moment.

The specific acuator model would help but in the meantime it is possible that the return spring in the actuator is damaged or there is some form of debri causing the actuator to bind. There may be corrosion on the valve step which the return spring can not overcome.

Thanks for the advice. Just a quick note to say that I think I've solved it. I'm using pins 14 and 15 now with a seperate 24v supply for the actuator. If I use pin 16 it gives a 240v output but the actuator is only 24v so can't us it. Basically the system is using the 4-20mA output from pin 15 and the com pin 14. I think this controller is not the best for the actuator.

The actuator is now moving in both directions and stopping in between but I have another problem. The actuator is only moving by a very small amount. I have tried increasing the proportional band but this has no effect. There is a auto function which I have switched on and this is better but it is still giving me a range from about 2.8-4.5 degrees with the set value at 3.5. Could anyone suggest a PID setup for getting a better response as the time over one cycle is in the region of about 15 min. Because the change in temp is so slow the valve should have no problem adjusting to compensate but it is only using a very small amount of the potential movement.

Please feel free to suggest any ideas or ask again if I haven't expressed myself clearly enough.

Thanks people.

There might be several reasons for that.

The controller may have output limit parameters. These keep the output modulating between two values only. Some do that to prevent unsafe conditions from occurring while some do it to keep the process from swinging wildly.

The second thing I would check is the calibration of the actuator positioner. Some positioners calibration deteriorate over time especially in the presence of vibration.

Next, I'd check the input measuring range. If the range is too large, your controller will not be able to respond quickly. Controllers depend on the value of the error. An error of 2°C on a measurement range of 0 to 100°C is equivalent to a 2% error whereas a 2°C error on a measurement range of 0 to 1000°C is an error of only 0.2%. A controller will provide a bigger adjustment for a 2% error than a 0.2% error.

Quick note to say this problem is now fixed. It turns out there were two problems. The first was that the wiring diagram from the chiller manufacturer was wrong. They had a 24v phase going to pin 15. This should have been the pin for the 4-20mA output. The second problem was that the controller was broken. I've replaced the SR-73 with another identical one which I pinched from a disused pasturising unit and it works fine.

Thanks to all especially Vulcan for your help.

Glad to be of service.

The 24V going into pin 15 must have fried the 4 to 20mA circuits. One thing about current signal outputs, there are two types: 1.) loop powered - this requires an external 24V supply to one of the two lines; 2.) self-powered - no power supply required for the current loop. The controller's power supply provides the voltage necessary for operation.

Your chiller manufacturer probably didn't read the controller's manual or didn't understand it. The right thing to do is to inform them of the error or else they'll be repeating the same mistake for their product. 'Might save a life somewhere.