HMI and 24 Vdc supply issue

[sayidengg 0]

Hi all, once again I have got an issue at my factory regarding another type of oven which is fully automated. It has got HMI panel with Allen Bradley micrologix 1500. This oven system has few motors which are run by Allen Bradley Powerflex 700 [ 12 pieces numbers]. Then this system has cutter mechanism which is microcontroller based [ 2 pieces]. The Allen Bradley PLC microlgix 1500 has Digital input and anolog output modules separate. There are few dc and ac relays in this system. Sensors are also included. This oven is standby type of oven, if the main oven fails or if the production is needed more, then this is brought in. Today, we have tried to start this oven. Its not letting HMI to power up even when the whole oven system is up. SMPS, which is feeding this system the supply of 24 VDC with 6 amps output[ 21 v DC tested @ o/p of SMPS with multimeter]. And we found out the VDC at the i/p of HMI to be 10V dc. So, what we did, is we gave differet direct 24 Vdc supply to HMI instead of the oven control system . It started up prefectly. Now, im wondering whether the smps is bad or should we check something else in this oven control system. Please let me what will be the 3way to deal with this type of situation. Thanks once agin all

[Shiner 2]

Usually partial votages are due to connection probelms. It could be a blown fuse that has some trace left, enough to carry small voltage but not enough current, or crimped insulation in connection points. Things like this can be missed if measuring on the terminal screws. If on one side of a terminal you have a good connection, you will read full voltage on the screw because it is a good connection. If the wire has insulation crimped into the clamp, the output will be affected. One key way to test a poor connection is to remove the connector that is supplying diminished voltage from the device. If your multimeter shows full voltage then you know you have a weak connection. The load of the device being plugged in will "pull" the voltage down due to the limited amount of current available. On the fuse part, I have seen people, and can feel more reading this shake their heads and say fuses don't blow like that. Unfortunately, I have come across installations where the fuse mounting played a part. Some solder element fuses are rated to melt and the solder fall to the bottom end of the fuse, breaking the circuit completely. I came across an installation where the fuses were horizontally mounted and the fuse had blown and enough trace laid across the bottom of the glass to allow a partial circuit. All of this simply put is this. You say your source voltage is correct means there is no problem with the power supply. You also say that your screen operates properly when a 24v source is applied to it so that means there is no problem with that. I would rebuild the entire circuit connecting the two. Remove, inspect and retighten each termination, replace any fusing, even if they OHM out ok! Edited 28 Mar 2012 by Shiner

[RussB 22]

If this were my system I would keep the dedicated power supply for the HMI and disconnect the original wires on both ends as there may be a break or short somewhere in the wiring and cause more problems later. Edited 28 Mar 2012 by RussB

[OkiePC 14]

What brand is the HMI? I looked up the specs for a Panelview 700+ a few weeks ago for a problem with a 5A power supply feeding power to two of them and several other devices (a Hirschmann switch and I think there were 4 NET-AIC modules). The PV700+ specs say "70W max (2.9 A at 24V dc)". We changed our set up so the two panelviews have their own 10A power supply and everything else that was tied to them runs on the original one. Edited 28 Mar 2012 by OkiePC

[sayidengg 0]

Thanks Sparky and OkiePC for your help. There was problem with faulty wiring , ground faults and also the sensor fouled. After rectifying these problems were able to use the old SMPS. OkiePC, the HMI we had in this system is not from Allen Bradley, as the OEM who built it got non Branded HMI . It mentioned for 24 Vdc though but was running with 21 VDC supply.