F-24853-4
©
Copyright 2006 TAC All Rights Reserved.
5
Table-2 illustrates the numbering scheme and software
assignments of the eight 0-11 Vdc analog inputs. When
making these assignments, the first entry is the option slot
number on the connection MSC-MPC controller and the
second entry is the number of the analog input being used.
For example, when plugged into option slot number 2, analog
input number 1 has an assignment of AI 21.
Table-2 Software Assignments for 0-11 Vdc Analog
Input.
INPNT = AI# (as shown below) /NOT
Calculating SCALE and OFSET Using MOCALC
MOCALC comes standard with the DOS Configuration Tool
and is used to determine the proper values for SCALE and
OFSET when provided with the desired values to be displayed
from given input parameters. MOCALC is typically used to
calibrate the display in engineering units in accordance with
measurements taken. In some cases it can be used to correct
for tolerance errors in input or output readings.
To use MOCALC, several parameters must be measured
prior to running the program. First, the physical property to be
measured or controlled is sampled near the high end of its
scale and the corresponding bit value is recorded.Then
another reading is taken with the property at the low end of its
scale and the bit value displayed by the system is again
recorded. Once this information is determined, the MOCALC
program is able to calculate the appropriate values for SCALE
and OFSET. Note that the characteristics of the variable must
be linear to use MOCALC.
The sample calculations below are for a Belimo SM24
Actuator with the P500 feedback option that will be used to
control a valve from 0 to 100 percent open.
For the point to be calibrated, set OFSET = 0 and SCALE =
4096.
With the feedback wired, drive the actuator/valve fully open
(100%). Record the measured bit value displayed by the
system for this point. This is the “bit high value”. Next, drive
the actuator/valve fully closed (0%). Record the measured bit
value again. This is the “bit low value”.
You are now ready to execute the MOCALC program.
1. From the C:\XCM directory, type MOCALC and press
ENTER.
2. At the enter number prompt, type 1 to select Formulas for
Scale and OFSET.
3. At the Enter Number prompt, type 6 to select Formulas for
Bit High...Bit Low.
The program prompts you for the device range high and range
low values. These values are the range of the points display,
which in this case is from 0 to 100 percent (open). You will
also need to enter the recorded bit values when the actuator
was driven to these two positions. MOCALC will then compute
the proper SCALE and OFSET for the point to display linearly
across the actuator’s travel range.
Please Enter Device Range High Value
Number:
100
Please Enter Device Range Low Value
Number:
0
Please Enter Recorded BIT HIGH Value
Number:
3298
Please Enter Recorded BIT LOW Value
Number:
517
SCALE:
147.28
OFSET:
-18.59
In the example above, the desired display range for the
actuator is 0 to 100 (percent open). The corresponding low
and high bit values were recorded as 517 and 3298,
respectively.
MOCALC determined SCALE to be 147.28 and OFSET to be
-18.59.
The formulas used by MOCALC are as follows:
SCALE = 4096 * (RANHI - RANLO)
(BITHI - BITLO)
OFSET = RANLO (SCALE * BITLO)
4096
Option Slot # On The MSC-MPC Controller
AI#
1
2
3
4
AI1
AI 11
AI 21
AI 31
AI 41
AI2
AI 12
AI 22
AI 32
AI 42
AI3
AI 13
AI 23
AI 33
AI 43
AI4
AI 14
AI 24
AI 34
AI 44
AI5
AI 15
AI 25
AI 35
AI 45
AI6
AI 16
AI 26
AI 36
AI 46
AI7
AI 17
AI 27
AI 37
AI 47
AI8
AI 18
AI 28
AI 38
AI 48
SCALE
OFSET
CVTYP
11
0
LIN 1
