DC/DM points in subLAN devices

Issue

Technical Support Services occasionally receives calls concerning the use of DC/DM points in the Micro Regulator product line. The use of DC/DM points in MRs is possible but only when certain guidelines are followed.

Product Line

TAC I/NET

Environment

  • SubLAN controllers
  • MRs
  • UCs

Cause

The functionality of the DC/DM points depends on what is actually controlling the DC point. If you use any of the extensions that reside only in the MRI, MCI or I/SITE LAN, etc., to control the DC point you will not have a problem. These extensions include: Time Scheduling, Temperature Control, Calculations and Event Sequences . As long as one of these editors controls the state of the DC point you should not see a problem with the functionality of the DC/DM points. Where you run into trouble is when an MR resident editor controls the DC point. These include all of the modules found in the MR Resident DDC editor, (PID, Floating, Two Position, Relay, Reset, Calculation module). If the state of a DC point is controlled by any of the MR resident DDC modules the associated DM point will always alarm in one state or the other.

The same is true for the UCI/UC product line in that a DC point can not be controlled by a UC resident editor. This includes everything under the Unitary Control editor, (VAV, AHU, PID, FLT, HPMP ). In fact, currently if an attempt is made to enter a DC point in any of these editors an error is generated which will not allow such an entry, (this error is not generated in the MR Resident DDC editor).

Resolution

If you need positive feedback like that provided by the DC/DM points please follow the guidelines set below:

  1. Create Control Description and State Description Parameters: Refer to figure 1 and 2.
  2. Create an External DO point for Fan Control. Refer to Figure 3.
  3. Create an External DI point for Fan Status. Refer to Figure 4.
  4. Create an Internal DA Point for Fan Alarm. Refer to Figure 5. 
  5. Create a Calculation for the DA point: Refer to Figure 6.

Anytime the Fan Control DO and the Fan Status DI follow each other’s state, the calculation remains True. If the DO does not equal the DI State, then the calculation becomes False. This results in an Alarm after the Time Delay of the DA has been met. The Time Delay acts in the same manner as the Time to State for a DM point. Please note if the DI 0 state was ON (the opposite of the DO), the calculation would be P0=~P1 .

 

*MSG* 09/21/95 12:34:29 Thu Control descriptions and commands
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798]
Enter up to 4 characters:
 # Description Command Delay
--+-----------+-------+-----
 0 STRT 1 0
 1 STOP 0 0
 2 0 0
 3 0 0
 4 0 0
 5 0 0
 6 0 0
 7 0 0
 8 0 0
 9 0 0
10 0 0
11 0 0
12 0 0
13 0 0
14 0 0
15 0 0

Figure 1: Control Description and commands

*MSG* 09/21/95 12:35:14 Thu State descriptions
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798]
Enter up to 4 characters:
 # Description # Description
--+----------- --+-----------
 0 OFF 16
 1 ON 17
 2 ALRM 18
 3 NORM 19
 4 20
 5 21
 6 22
 7 23
 8 24
 9 25
10 26
11 27
12 28
13 29
14 30
15 31

Figure 2: State descriptions

*MSG* 09/21/95 12:36:19 Thu Resident I/O points
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798] Point 0000 (02290000 DO)
Enter up to 16 characters:
Parameter Value Parameter Value
---------------------------------------- ------------------+--------
Point name Fan Control Distribution group 1
Point class Ext Distribution mask --------
Scan interval (seconds) 60 Alarm priority -
Global level Local Message priority -
State description 0 Cell number 0
Control description 0
Restart control action Reinforce
Minimum trip (minutes) 0
Minimum close (minutes) 0
Three-state output N

Figure 3: Resident I/O points

*MSG* 09/21/95 12:36:19 Thu Resident I/O points
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798] Point 0000 (02290000 DI)
Enter up to 16 characters:
Parameter Value Parameter Value
---------------------------------------- ------------------+--------
Point name Fan Status Distribution group 1
Point class Ext Distribution mask --------
Scan interval (seconds) 10 Alarm priority -
Global level Local Message priority -
State description 0 Cell number 0
Number of bits 1
Supervision None

Figure 4: Resident I/O points

*MSG* 09/21/95 12:38:56 Thu Resident I/O points
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798] Point 0009 (02290009 DA)
Enter up to 16 characters:
Parameter Value Parameter Value
---------------------------------------- ------------------+--------
Point name Fan Alarm Distribution group 1
Point class Int Distribution mask Y-------
Scan interval (seconds) 10 Alarm priority Priority
Global level Local Message priority Priority
State description 2 Cell number 0
Number of bits 1
Normal state 1
Alarm delay (seconds) 120
Supervision None

Figure 5: Resident I/O points

*MSG* 09/21/95 12:39:57 Thu Calculations
Host 00 (CSI) Link 02 [78020] DCU 29 [DCU 7798] Point 0009 (Fan Alarm)
Enter point address or name:
 Equation
---------------------------------------------------------------------------
P0=P1
Operand Point Operand Constant
-------+---------------- -------+----------------
P0 Fan Control
P1 Fan Status

Figure 6: Calculations

 

The above calculation will return the following DA conditions depending on the state of the DO and DI

DO DI DA
OFF OFF NORM
ON OFF ALRM
OFF ON ALRM
ON ON NORM