Instructions
The component failure alarm is a safety feature that alarms under three conditions:
1. Flow Indication Alarm
The system alarms if there is flow going through the meter after the batching operation when there should be no flow. A good example of this would be if the valve controlling the size of the batch leaked or failed, the meter would continue turning and would send electrical pulses to the batch system. The system then activates the alarm light and buzzer. Since an extra pulse or two might not be critical and could be caused by variations of the system, an alarm set point is incorporated in the system which inhibits the alarm until a predetermined number (up to 9) of extra pulses are received by the system. This number is variable and can be dialed into the controls by the operator by changing the number on switch number S-9. If a scaler is utilized the component failure alarm system receives pulses after they are scaled. This alarm can be silenced by pushing the alarm reset switch. This will clear only an over-flow type alarm condition. If switch S17 is changed to the up position the alarm over-flow counter will receive pulses from the totalizer divider circuit. The totalizer divider circuit is normally set to divide by 10; however, it can be changed to divide by 100, 1000, or 10000 via switch S18.
2. No Pulses Detected By Flow Element Alarm
The second alarm operates if the meter is not sending pulses to the system when it should be. A good example of this would be if a turbine or positive displacement meter becomes jammed and will not turn over, but flow continues through the meter without being metered. The system activates the alarm light and buzzer while it is not receiving pulses from the meter and the controls are in batching mode.
3. Low Flow Alarm
The last alarm is at low flow. This alarm pulsates each time a pulse is received from the meter when the flow rate through the meter is below a field adjustable predetermined rate of flow. Unless otherwise directed the EBU is factory set to alarm if the time between pulses going to the LED display is longer than 2.5 seconds. The flow rate at which the alarm is actuated can be changed by turning the potentiometer screw P1 either clockwise for alarm at a higher flow rate or counter-clockwise to have the system alarm at a lower flow rate. The minimum alarm time setting is about ½ second between counts. The maximum alarm time setting is 13 seconds between counts before the alarm sounds.
All standard control boxes have two digits of floating zero (switches S6 and S7). In liquid metering applications floating zero is necessary since it takes time for a valve to close, and during that time a quantity of liquid will be batched, greater than set on the EBU. For any liquid at any one flow rate that quantity is constant and the amount can be dialed into the floating zero circuitry of the controls. From then on the valve will close sooner to accommodate that amount of over-run.
The floating zero switches S6 and S7 correspond with the first two digits of the LED counter, with S7 being the least significant digit. The CR1 relay is energized at the beginning of the batch and is released when the LED counts down to the floating zero set point. If the EBU is operating in 1/10 gallons the maximum floating zero setting will be 9.9 gallons.
Suppose that it is desired to batch exactly 100 pounds of water into a kettle. 100 is set on the EBU and the start switch is pushed. The controls receive one electrical pulse from the flow meter for each pound of water that goes into the kettle, and once it counts 100 pulses it releases the solenoid that holds the valve open, allowing the valve to close. During the time that it takes the valve to close, three additional pounds of water go into the kettle, giving a batch of 103 pounds when only 100 pounds was set into the controls. The over-run will be shown on the EBU’s LED display when the over-run indicator is on. To prevent this from happening in the future, it is necessary to dial 3 on switch S7 and 0 on S6. From then on the valve will start closing 3 pounds short of the quantity set in the preset.
This feature can also be used instead of two-stage closure (or prewarn) to prevent water hammer (or shock) in the piping, caused by the valve closing too rapidly. A needle valve or orifice can be placed on the controls of the valve to slow the closure of the valve, eliminating most of the shock. This slow closure will increase, considerably, the amount of liquid going into the kettle. The floating zero feature will compensate for this overage so that the amount batched into the kettle will always be that set on the control box.
The batch size must be larger than the floating zero set point or the EBU will release the CR1 relay at zero.
The optional scaler consists of multiplication and division circuitry. Switch S12 controls multiplication. Switch S12 consists of four individual switches. Only one of the four should be on at a time. Should two or more be on, the scaler will give an incorrect output. When the first switch is on there is no multiplication of the incoming pulse. When the second is on, each incoming pulse is multiplied by 10. When the third is on, each incoming pulse is multiplied by 100, and when the fourth is on, each incoming pulse is multiplied by 1000.
Switches S13, S14, S15 and S16 do the division. Each switch can be set at any number between 0 and 9. Switch S13 divides by thousands, S14 by hundreds, S15 by tens and S16 by units. If switches S13 through S16 are set at 1110 and switch S12 is set at position 4, each incoming pulse will be multiplied by 1000 and divided by 1110. Consequently each time one pulse is put in the scaler, 0.9009 pulses will be put out by the scaler.
Basically the scaler is nothing but an electronic gear train. Increasing or decreasing the setting on a scaler is similar to increasing or decreasing the number of teeth on gears.
In this particular setup each time a pulse goes into the board it is multiplied by 1000 and divided by 1110. In a gear train this would be the same as a 1000-tooth gear driving an 1110-tooth gear. If the meter is 1% in error and is under-registering (i.e., giving product away), it is necessary to increase the speed of the counter by 1%. Therefore the divisor is decreased 1% or from 1110 to 1099. The multiplier remains constant at 1000.
The following formula is useful to determine a new scaler setting once meter error has been established (scaler setting is another name for divisor setting):
| Existing Scaler Setting x (Preset Amount + Over-Run) |
| Amount That Actualy Flowed |
Usually with flow rates over 50 GPM (20 GPM in the case of water and some other thin liquids) line shock or water hammer due to valve closure can be eliminated using a slow-closure valve and the floating zero feature. For higher capacities a two-stage closure valve is necessary. This valve opens on a start signal from the EBU. A prewarn signal from the control unit partially closes the valve to throttle the flow sufficiently to prevent line shock on final closure of the valve.
Prewarn is available as an optional feature and can easily be field adjusted or set. When the prewarn option is utilized the floating zero function is eliminated. Switches S6 and S7 will now be used to adjust the prewarn set point. Switches S6 and S7 correspond with the first and second digits of the LED display. This means that an EBU operating in 1/10 gallons will have a maximum prewarn setting of 9.9 gallons. S7 is the least significant digit. When the prewarn option is utilized the CR2 control relay is installed. CR2 is energized when the LED display reaches the prewarn set point. For example, assume a 100.0 count batch is set on the EBU and 53 is set on switches S6 and S7 respectively. When the EBU is reset the CR1 relay will energize. When the LED counter counts down to 0005.3 the CR2 relay will be energized. Both relays will be released when the LED shows zero. The batch size must be higher than the prewarn setting or the CR2 relay will not operate.
Some prewarn valve operators require a delay time be built into the EBU to prevent CR1 and CR2 from energizing at the same time when the system is restarted from an emergency stop condition. If the EBU is stopped while in prewarn it will be necessary to wait 20 seconds prior to restarting to ensure correct operation of the valve.
