PROPORTIONAL BAND (P.BND)

Proportional controls are designed to eliminate the cycling associated with on-off control. A proportional controller decreases the average power being supplied to the heater, as the temperature approaches setpoint. This has the effect of slowing down the heater, so that it will not overshoot the setpoint, but will approach the setpoint and maintain a stable temperature. This proportioning action can be accomplished by turning the output on and off for short intervals. This ôtime proportioningö varies the ratio of ôonö time to ôoffö time to control the temperature.
The time period between two successive turn-ons is known as the ôcycle timeö or ôduty cycleö. The proportioning action occurs with a ôproportional bandö around the setpoint temperature. Outside this band, the controller functions as an on-off unit, with the output either fully on (below the band) or fully off (above the band). However, within the band, the output is turned on and off in the ratio of the measurement difference from the setpoint. At the setpoint (the midpoint of the proportional band), the output on-off ratio is 1:1 that is, the on-time and off-times vary in proportion to the temperature difference. If the temperature is below setpoint, the output will be on longer. If the temperature is too high, the output will be off longer.

Figure 16-1
Proportional Band

The proportional band is usually expressed as a percent of full input range scale, or in degrees. It may also be referred to as gain, which is the reciprocal of the band. In many units, the cycle time and/or proportional bandwidth are adjustable, so that the controller may be better matched to a particular process.

Proportional controllers have a manual reset (trim) adjustment, which may be used to adjust for an offset between the steady state temperature and the setpoint.

In addition to electromechanical and solid state relay outputs, proportional controllers are also available with proportional analog signal outputs, such as 4 to 20mA or 0 to 5 Vdc. With these outputs, the actual output level amplitude is varied, rather than the proportion of on and off times.
To select the proportional band for your proportional controller.

Note: "P.BND" only shows if you select analog output as proportional.
1. Press the MENU button until the meter shows "P.BND".

2. Press the /DEV button. The meter shows last previously stored 4- digit number (0000 through 9999) with flashing 4th digit.

3. Press the /MAX button to change the value of the flashing digit. If you continue to press the /MAX button, the flashing digit's value continues to change.

4. Press the /DEV button to scroll to the next digit.

5. Press the MENU button to store your selection. The meter momentarily shows "STRD", followed by "M.RST" (Manual Reset)

MANUAL RESET (M.RST)

Manual Reset (M.RST) is not active unless your meter has analog output and relay capabilities. The menu will display whether analog output is present or not. This feature allows you to offset the error that may occur with your setpoint. In order to determine the amount of error, you must compare your display value to the setpoint 1 value. The difference between these two values is the amount of error that you may want to enter into Manual Reset (M.RST).
Note: "M.RST" only shows if you select analog output as proportional.
1. Press the MENU button until "M.RST" displays.

2. Press the /DEV button. The meter shows the last previously stored 4-digit number (-1999 through 9999) with flashing 4th digit.

3. Press the /MAX button to change the value of the flashing digit. If you continue to press the /MAX button, the flashing digit's value continues to change.

4. Press the /DEV button to scroll to the next digit.

5. Press the MENU button to store your selection. The meter momentarily shows "STRD", followed also momentarily by "RST" (Reset).

Always choose the value of "M.RST" less than "P.BND/2". Meter will not accept larger values and displays with flashing "ER 4".

OUTPUT SCALE AND OFFSET ("OT.S.O")

Output Scale and Offset ("OT.S.O") is not active unless your meter has analog output capabilities. The menu will display whether analog output is present or not. Output Scale and Offset ("OT.S.O") scales your analog output to be equal to the meter's display and/or any engineering units you require. You may scale the output for direct (4-20 mA, 0-10 V, etc) or reverse acting (20-4 mA, 10-0 V, etc).
Note: "OT.S.O" only shows if you select analog output as a retransmission of temperature.
1. Press the MENU button until "OT.S.O" displays.

2. Press the /DEV button. "RD 1" (Read 1)
Note: This is your first point of display reading.

3. Press the /DEV button again. The meter shows the last previously stored 4-digit number (-1999 through 9999) with flashing 4th digit.

4. Press the /MAX button to change the digits.

5. Press the /DEV button to scroll to the next digit.

6. Press the MENU button to store your selection.The meter shows "OUT.1" (Output 1) displays.
Note: This starting analog signal corresponds to your Read 1 display.

7. Press the /DEV button. The meter shows selected output.

Note: If you select "O.2=V" for voltage, the maximum signal you may select is 10.00 for an 0-10 Vdc signal output. If you select "O.2=C" for current, the maximum signal you may select is 20.00.

8. Press the /MAX button to enter the Output 1 signal selection. If you continue to press the /MAX button, the flashing digit's value continues to change.

9. Press the /DEV button to scroll to the next digit.

10. Press the MENU button to store your selection. The display shows "RD 2" (Read 2).
Note: This is your second point of display reading.

11. Press the /DEV button. The meter shows last previously stored 4-digit number (-1999 through 9999) displays with flashing 4th digit.

12. Press the /MAX button to change the value of the flashing digit. If you continue to press the MAX button, the flashing digit's value continues to change.

13. Press the /DEV button to scroll to the next digit.

14. Press the MENU button to store your selection. "OUT.2" (Output 2)displays.
Note: This analog signal should correspond to your Read 2 display.

15. Press the /DEV button. Selected output displays.

Note: If you select "O.2=V" for voltage, the maximum signal you may select is 10.00 for an 0-10 Vdc signal output.

If you select "O.2=C" for current, the maximum signal you may select is 20.00 for a 0-20 or 4-20 mA dc signal output.

16. Press the /MAX button to change the value of the flashing digit. If you continue to press the /MAX button, the flashing digit's value continues to change.

17. Press the /DEV button to scroll to the next digit.

18. Press the MENU button to store your selection. The meter momentarily shows "STRD", followed also momentarily by "RST" (Hard Reset). Meter then returns you to the "RUN" mode.

Caution WARNING: If the meter displays all flashing values on any item, the value has overflowed. Press the /MAX button to start new values.
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