To provide smooth constant flow from a pump a feedback system comprises: a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for alternately energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.
A fast response control circuit for providing an output signal in miminum time after receiving an enabling input signal. The control circuit includes an amplifier which provides an output signal having a magnitude determined by a variable input signal when the enabling input signal indicates that an output signal is desired. A feedback network and the amplifier together define a control loop which has a characteristic response time. When the enable signal is absent, a bias control biases a reactive component in the control loop so as to minimize this response time. The circuit is adapted for use in a fluid mass flow controller to provide rapid response to an enabling input signal, particularly when a very low fluid flow rate is desired.
A system for detecting an occlusion in a fluid line is disclosed which can detect occlusions in the upstream or container side of a disposable cassette containing a fluid pump therein. The cassette includes a piston-type pump with inlet and outlet valves, and is for installation onto and use with a main pump unit including motors for driving the pump and valves contained in each cassette. The system utilizes control circuitry to monitor the intake stroke of the pump in the cassette, to detect an upstream occlusion in the fluid line leading to the pump, and to provide an alarm in the event of a container-side occlusion.
A control arrangement for a liquid chromatograph is disclosed which generates a correction factor to compensate for non-uniform passage of eluate past the detector of the chromatograph. A flow meter measures the actual flow of eluate from the detector and generates a representative signal which is compared with a standard signal representative of the desired flow rate to generate the correction signal.
There is disclosed herein a system for testing the flow stability of the pumping system for liquid chromatography. The system determines the flow rate and determines the number of revolutions over which the flow rate is to be measured from the flow rate. The system then measures the value of a signal which is related to the flow rate multiple times for each revolution. The maximum value and the minimum value for each revolution is recorded. After the data from the requisite number of revolutions is collected, a calculation is performed which determines the flow stability indicator which is displayed. The calculation takes a multiple of the difference between the maximum of maximums and the minimum of minimums and divides it by the sum of the maximum of maximums and the minimum of minimums.
A switching DC-to-DC converter comprising a controller to regulate a load voltage according to a set-point and a sample-and-hold circuit, the sample-and-hold circuit coupled to the controller to decrease the set-point of the controller if an average of current flowing through the inductor increases.
