Watson-Marlow Qdos30 Universal - Manual (Page 46)

Watson-Marlow qdos30 Universal and Universal+ Pump User Manual 46
16.2 Contact operating mode
To enter contact mode press the MODE key, move the selection bar to Contact, and
press SELECT.
The contact mode home screen will be displayed. The home screen displays the
contact dose, the flowrate, and the dose time remaining when a dose is in progress.
The dose time is only displayed on screen when it is between 3 seconds and 999
seconds.
When the pump is not dosing it is possible to manually start a dose by pressing the
START key.
Dose’s which operate for less than 3 seconds are not recommended.
Pulse dosing as an operation mode has its limitations. From an application perspective
it is often not the most efficient method of achieving concentration consistency due
to the pump only metering when a pulse is received, as opposed to continuously
running in proportion to the flow. Intermittently dosing into a fluid line will require
enough pipe to ensure the solution is adequately mixed, or a mixing tank.
With the ability to operate at very low speeds, metering chemicals is a much better
solution than dosing them at intervals. We recommend examining your process to
identify whether a 4-20mA signal can be used rather than a pulse. Where technology
does not allow a 4-20mA signal we recommend a using signal converter accessory.
This can be used to change your pulse signal to a 4-20mA signal, ideal for metering
(see 15.5 Analog 4-20mA mode on page 37).