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ATI A15/66 Residual Sulfite Monitor

O&M Manual

Rev-W (8/10)

PULSE FREQUENCY MODULATION (PFM) CONTROL

Relays A and B in the electronic monitor can be used for direct control of certain kinds of

metering pumps using a pulse frequency control mode. In pulse frequency control, the relay will briefly

close at a frequency linearly proportional to the deviation of the measured value from your setpoint. This

type of output is used when controlling a chemical metering pump that has a pulse frequency input from

an unpowered relay. To use PFM control, the relay must be configured for PFM control in steps 14 or 16

of the configuration menu. For chemical feed control, you will normally want to set the alarm relays to low

in steps 15 and 17.

To set up a control system using PFM control, you must program a setpoint, a proportional band,

and a frequency range. The setpoint is the maximum value that you would want to maintain. When the

measured value reaches the setpoint, the output frequency will stop. To set the setpoint, press the

MODE key until the display reads “SA X.XX PPM F L”. Then press the CAL key once. The display

will read “CAL SA S: X.XX”. Use the UP and DOWN keys to select the desired setpoint. Then press

ENTER.

The next setting is the proportional band setting. After pressing ENTER in the previous section,

the display will indicate “CAL SA BP: X.XX”. The proportional band is the amount of deviation from the

setpoint required for the frequency output to reach maximum pulses per minute. Use the UP and DOWN

keys to select the proportional band and then press ENTER.

The final setting is the maximum pulse frequency required to control the pump. You should check

your chemical feed pump manual to determine what overall frequency is recommended. The monitor can

be adjusted for full scale frequency outputs from 0-120 pulses per minute. When you press ENTER in the

previous step, the display will change to “CAL SA f: 100 i/m” This is the default setting of 0-100 pulses

per minute. Left at this value, the relay will pulse at 100 times per minute when the measured value at

maximum deviation from the setpoint and will not pulse at all when the measured value reaches the

setpoint. Enter the value you want for the maximum pulses per minute and press ENTER. The display

will flash UPDATE and the relay will begin to operate in accordance with the programming entered.

As an example, assume that you want to use relay A to control a metering pump feeding sodium

bisulfite. You would like to maintain a sulfite value between 0.5 and 1.0 PPM and your metering pump

input is 0-60 pulses per minute. Programming would then be as follows.

1. In the configuration menu, step 14, select PFM.

2. In the configuration menu, step 15, select LO

3. Go to the A relay display (display D4, page 20) and press CAL.

4. Adjust the setpoint value to 1.00 and press ENTER.

5. Adjust the proportional band value to 0.50 and press ENTER

6. Adjust the frequency to 60 and press ENTER.

With the programming just entered, relay A will pulse 60 times per minute when the measured

sulfite value is below 0.50 PPM. When the value reaches 0.75 PPM, the relay will be pulsing 30 times

per minute. When the value reaches 1.00 PPM, the relay will stop pulsing.

You can verify the operation of the relay by placing the monitor into simulate (SIM) mode of

operation. By manually increasing or decreasing the displayed value, you will hear the change in the

relay pulses. Note that the “” symbol indicating the relay condition will pulse each time the relay closes.

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