Beck, R&J ELECTRIC ACTUATORS FOR INDUSTRIAL PROCESSCONTROL 11-1_9 Manual Do Utilizador

57

 

DCM-2 boards are designed to accept a 

4–20 mA (or 1–5 V dc) analog Demand signal.  
Narrower spans within this range can also 
be accommodated for split range operation 
(see explanation following).  The input comes 
calibrated from the factory for the full range 
unless otherwise specified.  It is not necessary 
to calibrate the Demand input when the drive is 
installed. 
 

If the Demand must be changed, it is 

accomplished using a HART comunication 
device.
 

First, navigate to the Configuration menu.  

Select the Demand Setup submenu.  Through 
this submenu, the Demand range limits and 
curve specifications may be changed.  Online 
help is available through the communication 
device.

DCM-2 HART INTERFACE

 

It is sometimes desirable or necessary to have 

more than one final control element controlling 
a single process.  Often, this type of control 
strategy requires that two to four Beck drives 
each respond to different portions of one 4–20 
mA Demand signal from the control system.  
 

This type of operation is called split range 

operation.  For example, consider the most 
common split range scenario—two drives split 
ranged for 50% of the 4–20 mA Demand signal 
input.  Both drives are wired in parallel to receive 
the same 4-20 mA signal (note that the total loop 
resistance should be 250 Ohms as specified by 
the HART

®

 communications protocol. The 250 

Ohm R11

 

resistor (see DCM-2 illustration on page 

78) must be removed from one of the two drive 
DCM-2 boards to allow HART

®

 communications.  

If more than two drives are split ranged, the R11

 

resistor must be removed from all the DCM-2 
boards but one), but each drive’s interpretation 
of the signal must be different.  One drive must 
interpret 4–12 mA as 0–100% Demand, and 
one drive must interpret 12–20 mA as 0–100% 
Demand.  This requires that the drives have 
different Demand signal calibrations.
 

Split-ranging is easily accomplished by 

determining the break points (12 mA in the 
example above) and using a HART communication 
device.  
 

First, navigate to the Configuration menu.  

Next, select the Demand Setup submenu.  
Change appropriate Demand range limit 
accordingly.  In the example above, one drive's 
upper Demand range (DemRngUpr) would be 
changed from 20.00 mA to 12.00 mA; and the 
other drive's lower Demand range (DemRngLwr) 
would be changed from 4.00 mA to 12.00 mA.