When communicating in DE mode, the DE protocol modulates a 4-20mA signal, where logic 1 is 20mA and logic 0 is 4mA. This is a very powerful digital data communication method, but the speed is slow.
Select (configure) DE mode or 4-20mA mode to communicate with the receiver. One or more process variables (primary, secondary, etc.) can communicate digitally at a relatively low rate in DE mode, approximately 2-3 PV values per second. The alternative 4-20mA mode is only used for configuration or troubleshooting, where the process variables (PV) of the instrument communicate with traditional 4-20mA signals, but DE modems or handheld communicators can sometimes be used to query DE smart devices.
When connected to the device for the first time, the software/modem or handheld device displays a warning to the user to “place the loop in manual (mode)” mode, as if the loop is in automatic mode, the de mode communication will oscillate the 4-20mA signal used for process variables and cause sustained interference.
The only receiving device that uses DE is Honeywell’s early DCS system.
The field instruments using DE include Honeywell ST3000 series pressure, temperature, and magnetic flow transmitters from the 1987-2015 era, as well as Honeywell’s current Smartline transmitter, which has a tab for DE communication. The pressure and flow meter of Azbil (formerly Yamatake) continue to follow the DE protocol.
