Digital flow totalizers, batch dispensing, and analog alarms
Digital flow totalizer
Alicat’s integrated digital flow totalizer (TOT) is an optional function that can be used to precisely measure the total amount of gas or liquid that passes through your Alicat flow meter or flow controller. Adding a totalizer to a controller means you can use batch mode to dispense fluids in set quantities.
This option adds an additional mode screen that displays the total flow that has passed through the device on a 7-digit counter, as well as the elapsed time since the last reset in hhhh:mm:ss format. The totalizer also displays the current flow rate and the peak flow rate since it was last reset.
A totalizer ordered without adjustments (TOT) has the following defaults:
- Decimal place: On older devices, this defaults to the same decimal place as the instrument flow range. If you have a 50 SLPM flow meter with a resolution of 50.00 SLPM, then the maximum value of your flow totalizer before it rolls over will be 99999.99. On newer devices with higher resolution, the totalizer will typically have one less digit after the decimal. This can be changed to a different resolution upon request.
- Units: Same as flow rate. Totalizer units can be changed in the display menu.
- Flow type: Displays mass flow total. Volumetric flow totalizers are available upon request.
- Rollover: Rolls over to 0 and displays “OVR” as a warning that the totalizer has rolled over. Alternatively, we can program the totalizer to roll over without displaying an error at all, or to freeze the totalizer counter when it reaches the maximum count and display the OVR error.
Note: If your totalizer displays a “TMF” error, this means that the totalizer missed counting some of the flow because the maximum measurable flow rate of your instrument was exceeded at some point during the totalization period. Reset the totalizer and ensure that the max flow rate is not exceeded.
Bidirectional flow totalization
If you are expecting flow to occur in both directions through your flow meter or an MCD bidirectional flow controller, there are several ways to handle the negative flow readings:
- TOTBD1 subtracts negative readings from the flow total.
- TOTBD2 subtracts negative readings from the flow total, but the total itself can never be lower than 0.
- TOTBD3 ignores negative readings; the flow total includes only positive flow readings.
- TOTBD4 ignores negative readings and resets the totalizer each time flow crosses 0. The flow total includes only positive flow readings.
If you need to obtain an averaged flow reading over time instead of (or in addition to) the total amount that has flowed, you can order your totalizer with flow averaging (TOTAVG). This feature enables the totalizer to average the total amount flowed since the last reset. Flow averages update in real time just as fast as live flow rate readings update (1000 readings per second).
This feature is especially useful when you need to know the flow rate of an instrument that is oscillating, such as a pump. Simply reset the totalizer and record your reading once the value stops changing.
The Precision Dispensing Package (available for controllers by requesting the TOT option) takes advantage of our fast proportional control valves and totalizer functionality to enable batch processing. Users may dispense gas or liquid volumes at their desired flow rates by means of independently controlled batch values and flow rate setpoints.
This function works much like the pump at a gas station; simply choose the total amount that should be dispensed and your desired flow rate. Your flow controller will automatically close its valve once the setpoint has been reached. You can start another batch of the same size by pressing the RESET button.
Full batch control and totalizer data are also accessible via serial communications.
Analog signal alarms
Many Alicat instruments can accommodate a secondary analog output signal that can be set at the factory to function as a flow or pressure alarm. High analog flow or pressure alarms (ALH) send the specified output signal if the flow or pressure exceeds the alarm setpoint. Similarly, the low analog flow or pressure alarms (ALL) send the specified output signal if the flow or pressure drops below the alarm setpoint. ALL and ALH setpoints must be defined at the time of order.
Available output signals for analog alarms
- 5 Vdc (default) output (ALL5 or ALH5)
- 12 Vdc output (ALL12 or ALH12)
- 24 Vdc output (ALL24 or ALH24)
- 500 mA open drain output (ALLOD or ALHOD)
Pulsed analog output
Pulsed analog output (PUL) causes your Alicat gas or liquid flow controller to function as a simple totalizer. This option pulses the output between no signal and full signal each time half of the specified flow has passed through your instrument.
For example, consider a gas mass flow meter ordered with PUL: 100 SCC and a 5-volt analog output. Once flow begins, the secondary output would emit 0 volts until the flow total reaches 50 SCC. At this point, the secondary output signal switches to 5 volts and remains there until 100 SCC is reached. At this point, the signal returns to 0 volts, and the cycle can be repeated.