PDSIO™
Pulse Density Signaling I/O

A new, patented technology from Eurotherm Controls

PDSIO is a "smart interface" which passes additional control loop status data transparently on the same wires which carry the primary analog or logic control signals. This permits bi-directional communications to occur on top of the standard control signals which might be a 4-20 mA output or a >6VDC logic pulse for solid state relays.

This bi-directional communication method is not another digital communications protocol. This method does not require an external smart I/O interface. PDSIO does not require special software drivers.

PDSIO is available as several different modes depending upon the application. These modes are as follows:

SSRx Load Doctor™ Diagnostics

Also called PDSIO Mode 1 capability:
 
MODE 1: CONTROLLER TO SOLID STATE CONTACTOR 
The Series 2000 controller sends on/off signals to the PDSIO-ready TE10S solid state contactor which represent "turn on or off". The contactor also monitors its health status and transmits this back to the controller. The SSRx Load Doctor circuit will signal a fault (called LdF, Load Fault) when any of the following conditions occur: blown fuse, open heater, contactor failed in "on" state, contactor failed in "off" state, wiring to heater "open", or wiring to contactor "open". In summation, did the current flow, or stop flowing, as requested by the Eurotherm Series 2000 controller?
The LDF software alarm flashes on the face of the Series 2000 controller and a red LED activates on the appropriate TE10S contactor. In addition, this feature can trigger an alarm relay or it can be communicated to a PC/PLC via EIA 485 communications.

SSRx Enhanced Load Doctor™ Diagnostics

Also called PDSIO Mode 2 -- CONTROLLER TO SOLID STATE CONTACTOR

This mode is similar to mode 1 plus it monitors the current (amps) of the heater load. The contactor health status and the analog current data are transparently transmitted back to the Series 2000 instrument. No external CTs, current monitoring devices, or extra wiring are required. This feature eliminates ammeters, CTs, and fuse failure indicators, extra wiring and extra installation time. The diagnostics information (amperage and health status of the load or contactor) is displayed at the local Series 2000 controller and it can be communicated to supervisory computers as a parameter on an EIA 485 communications link. The SSRx Enhanced Load Doctor supplies 3 types of data -- amperage of the load, SsrF failures that represent constant current flowing (failed "on"conditions), and HtrF failures that represent no current flowing (failed "off"conditions). Either condition can be independently alarmed or they can be combined onto one alarm relay output.

The Series 2000 instrument displays the amperage information. The amperage data is stored in a short term (25 second) memory location in the instrument so the display will be a constant number (such as: 30, 30, 30 amps). This is done so that you can trend this information if your instrument is communicating to a SCADA system. This is a tremendous benefit compared to other methods where the amperage is shown cycling (30, 0, 30, 0 amps). The Eurotherm memory method plus the load alarms provide a complete "Enhanced Load Doctor" health check of your load circuit.

SST Smart Setpoint Transmission™

Also called PDSIO Mode 4 -- CONTROLLER TO CONTROLLER communications
Sometimes referred to as peer-to-peer, client/server, or master/slave communications.

The PDSIO technology permits a master "ramp/dwell/ramp/dwell/...." controller to re-transmit the program to multiple adjacent slave controllers over a 2 wire daisy-chained cable. The transmitted signal has the accuracy of a digital signal without the complexity of a digital protocol. If one of the slave controllers fails to follow the program, a "hold the ramp/dwell program" command is instantly transmitted back to the master, via the same 2 wire cable, until the condition clears. Multiple slave instruments can be connected without any degradation with the SST signal. Contact Eurotherm to discuss how to connect 1-XX slave instruments.

SDI Smart Digital Input™

Also called PDSIO Mode 5 -- Digital Input Usage

The Series 2000 instruments have two "digital inputs" as standard in the 1/8 din and 1/4 din instruments. This includes the 2208, 2204, 2408 and 2404 instruments. Normally, these digital inputs permit a contact closure to activate a software function that had been assigned to that input (for example: select setpoint 2, activate self-tune, run the program, go to manual output, etc). The SDI capability permits these digital inputs to also accept analog information that is being transmitted from SDI compliant products. For example, the Eurotherm PD/CTX product acts as a CT (current transformer) in order to read amperage when used with existing mercury or mechanical contactors applications. This analog amperage information is converted to high accuracy, high speed digital pulses which can be connected directly to the existing digital input terminals on the Series 2000 instruments.

AN-CTL-30: Description of PDSIO™ Principles