Pump-switching program

Four different types of tasks are performed by automation. Two involve the sequencing of valves and pumps Involved 1n the setup and completion of the designed experiment through the operation of the test and hydraulic fluid systems. The other tasks involve the control of the temperature bath and data collection. To perform these tasks, a1r-actuated solenoids and optically coupled sol Id-state relays are used. These devices are controlled by an electrical circuit consisting of the device connected 1n series with a power supply and a channel on the actuator card In the HP 3497. The power supply 1s either 24 VDC for use with the solenoids or 5 VDC for the solid-state relays. The actuator output channel acts as a simple on/off switch which allows power to be supplied to the solenoid or relay when closed. The logic of the circuit 1s controlled by application programs running on the local HP 1000. 

Integrating liquid-liquid extraction and detection is far from easy, as reflected in the few attempts made so far. Many of the devices developed for this purpose fail to comply with the definition of sensor. Such is the case with continuous liquid-liquid extraction systems without phase separation, where programmed switching of the propulsion system (a peristaltic pump) allows the extracting phase to be passed iteratively by the detection point in a back-and-forth motion that enriches it gradually with the extracted species [9-11]. This type of system is much too Complex to be considered a sensor, though in addition, the extraction process is not completely simultaneous with detection. 

The front panel of the controller has two four-digit thumbwheel switches and two lighted pushbutton switches. The thumbwheels determine flow rate (ml/min) and volume to be delivered (ml). One pushbutton switch initiates the pump-refill operation. The other starts the injection, or stops an injection in progress. After power-up or reset, the microprocessor initializes itself and sets up the timing module and serial ports. It then jumps into a looping program that scans the two pushbutton switches and the... 

Another part of the loop program ascertains how much solution is left in the pump. A voltage picked off a ten-turn potentiometer, which is coupled to the piston-drive screw with a timing belt, is fed to the analog-to-digital converter and is compared with the previously stored reading from the thumbwheel switch. 

In computer systems, program logic is an important component of the critical instrument loop. Security precautions must be taken to prevent inadvertent changes in programming. In addition, manual overrides are discouraged. For example, if it is critical to shut down a pump during an emergency situation, a manual on switch may not be desirable. 

The flow rate of the dissolution medium through the cell must be specified for each product. The USP recommends a flow rate between 4 and 16ml/min with an allowance of 5%. Manual operation and sampling for this type of test can be tedious and the system can be automated to control the pump, heat exchanger and test procedure, and deliver samples to a fraction collector. The system can be programmed to switch between different media at predetermined time points to allow pH changes during the test. 

The results of a therapeutic interchange program, in which 78 patients with acid peptic disease requiring proton pump inhibitor therapy (both newly diagnosed patients and those previously stabilized on omeprazole) were treated with lansoprazole, have been retrospectively analysed (12). Although the switch was associated with considerable pharmaceutical savings, there was an overall lansoprazole-associated failure rate of 28%. Reported lack of efficacy required withdrawal of lansoprazole in 15%, while adverse effects required withdrawal of lansoprazole in 13% of patients (versus none with omeprazole). The main adverse effect was diarrhea. 

If a detector without a programming option is used, switching can be carried out manually or by another programmable component, e.g. the pump. 

Figure E18-2. Pump controller (1) on/stby switch, (2) programming keypad, (3) softkeys to select menu items,...

Programming of a robot is based on software dedicated to the actual manufacture. The software consists of elements to control the peripheral devices (robot arm, balance, pumps), to switch the devices on and off, and to provide instructions on the basis of logical structures, for example, IF-THEN rules. 

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