brycebsp

Twisted shielded cables are being used for all analogs (4-20mA's) there are some Relay outputs from the VFD's that are 120V and run in seperate conduit. These were the wires I was talking about changing to shielded as well. I have several spare Analog in's and outs that are being used. They are essentially sitting there open. Could terminating these make a difference? If so what is the proper way to terminate them? To CLAYB yes the motors ramp up and down as required to flow match. Have been using this Brand of VFD for over 5 years with very few failures. I really had hoped the DVDT filters would have resolved my problem since the noise seemed to only be present when the drives have a load on them. Thanks for the input so far. Bryce

Thanks all. I will investigate where the motor ground is connected when I go to site next. From memory I believe the motor ground goes to copper ground lug on the VFD enclosure back plate and then is bonded by a wire from there back to the VFD ground. The motor does not have shielded motor cables. The motor is part of a submersible pump therefore Submersible motor cable is used from the pump back to the VFD. The motor is 45HP and as I mentioned earlier the VFD's are each in their own cabinets seperate from the control equipment. Of course there are some control connections between the VFD and the control system. Control wiring is in a seperate conduit from the motor leads and all conduits are galvanized and grounded. I am thinking about changing out all the control wires to twisted shielded to see if that makes a difference. Any additional thoughts are appreciated.

I would recommend Siemens (Milltronics) or MJK Shuttle. http://www.mjk.com/index.php?id=1065 Bryce

Hello all. First time poster. I am hoping someone here can offer some advice or a solution to a problem I am having. I am working on a system that consists of a control panel (With PLC and HMI) and located adjacent to the control panel is two VFD's in their own enclosures. All the enclosures are steel. On the PLC there is a mixed analog I/O module with 4 (4-20mA) inputs and 4 (4-20mA) outputs. I am using one input connected to hydrostatic pressure transmitter for measuring water level. I am using two outputs from the module to send speed reference to each VFD. The problem that I am having is that when the VFD's are running with a load my analog input bounces around. If I go into the register for the analog input and watch the raw value it will randomly jump up or down as much as 100 points. The resolution of the analog input is 12bit (0-4095 raw value). I have tried disconnecting the transmitter and feeding a steady mA signal from my Fluke process meter and I still have the same problem. Example... I fed a steady 12mA in and start the VFD's signal begins to bounce around. Shut off VFD's and bounce stops. Things I have tried so far.... 1. Checked grounds for good connections and potential ground loops (SEVERAL times) 2. Replaced Analog Module. 3. Replace entire PLC 4. Added DVDT filters to the outputs of the VFD's. 5. Added rungs of logic that do a 3 sample average of the analog input in hopes of quelling the size of the bounce. 6. Tried an Allen-Bradley PLC instead of the one I am currently using (EZ-Automation) and had the same problem. 7. Tried connecting .01 microfarad caps inline with shields on 4-20mA circuits. 8. Replaced 24VDC power supply. Other things to note: all the analog signals that go in or out of this analog module go through Dataforth DSCL22 isolators. Also if I disconnect the motors from the VFD's (no load) and ramp the drives up and down I have no problems. The entire system is mounted on a steel platform mounted 15' in the air. It is located adjacent to a river so the idea is to have the control equipment above flood levels. I feel like this big steel platform is acting like a giant antenna and causing my problems. I realized this is difficult for anyone to solve via e-mail. I am just hoping some of you can make suggestions of additional things to try.