Maintenance Man
Member
Hi to all. We have a pH transmitter from Mettler Toledo (M400) that can be powered by 120 VAC or 24VDC. We also have a transmitter (M420) that is powered by 24 VDC loop power. I was going to install a M400 as a temporary set up until we got another M420 in. I set up the M400 in the shop using a dc power supply set to 24 VDC. When I tried to hook it up in the field on the 24 VDC loop it would not come on. My DC meter was reading 24 VDC in the field on the loop power. To make a long story short, I am wondering what the difference between 24 VDC and 24 VDC from a power loop. The power loop also has the 4 – 20 mA imposed on it for the Hart function. The power loop is on our DCS. Any help to understand the difference would be greatly appreciated.