Transfer, auto-manual

Process-variable feedback for the controller is achieved by one of two methods. The process variable can (I) be measured and transmitted to the controller by using a separate measurement transmitter with a 0.2-I.0-bar (3-15-psi pneumatic output, or (2) be sensed directly by the controller, which contains the measurement sensor within its enclosure. Controllers with integral sensing elements are available that sense pressure, differential pressure, temperature, and level. Some controller designs have the set point adjustment knob in the controller, making set point adjustment a local and manual operation. Other types receive a set point from a remotely located pneumatic source, such as a manual air set regulator or another controller, to achieve set point adjustment. There are versions of the pneumatic controller that support the useful one-, two-, and three-mode combinations of proportional, integral, and derivative actions. Other options include auto/manual transfer stations, antireset windup circuitry, on/off control, and process-variable and set point indicators. 

To ensure a bumpless transfer from manual to automatic, the manual output signal, indicated by the output meter, is adjusted to match the controlled variable value to setpoint. This will be indicated by no deflection of the deviation meter. Once matched, the M-A transfer switch can be switched from manual (MAN) to automatic (AUTO) control. 

Apply an input signal to the loop controller equivalent to 50% of the instrument range and adjust the output of the manual pneumatic regulator to 50%. Adjust the loop controller setpoint to 50% and, by switching the auto/manual transfer switch, check for bumpless transfer. Using the manufacturer s instructions, adjust where necessary until a satisfactory bumpless transfer is achieved. 

There is no reason for auto-manual transfer switches in any of the con trollers, if there is a transfer switch at the output of the selector. Because of the common feedback circuit, transfer to manual at that point, will not cause windup. 

Some samples lend themselves to small column cleanup such as that provided by Waters Sep-Pak (a miniature chromatographic column). And several suppliers offer processing turntables which will perform various cleanup operations which are frequently required prior to chromatography. And when samples have been cleaned up (whether manually or by one of these automated devices), they can then be transferred to an HPLC unit by any one of several available auto-injectors. 

Because SPME is a single-step technique — which minimizes sources of random errors associated with transfer of the analytes — it exhibits very good precision with clean, model samples. In fact, the precision of SPME is typically in the region of 5% (as RSD) with manual operation and can be as low as 1% with model samples processed using an auto-sampler. On the other hand, complex matrices and carry-over effects can result in RSD values as high as 92% [226,227],... 

IQ Proper installation of system Correct software version All parts are present and connected correctly Software virus check Integrity of hard disk Availability of source code, manuals OQ Start -up routine Calibration routine Data transfer/backup Data integrity Power failure Auto lock off Human-machine interface Security access/audit trail System Stress test in event of power failure Alarm tests... 

After all experiments are finished the whole fraction collector/auto sampler rack is transferred manually to the HPLC autosampler. When the HPLC runs are finished the chromatograms are sent back to the controlling computer for analysis and generation of the required reports. 

When a cascade control system is tuned after installation, the secondary controller should be tuned first with the primary controller in the manual mode. Then the primary controller is transferred to automatic, and it is tuned. The relay auto-tuning technique presented in Chapter 12 can be used for each control loop. If the secondary controller is retuned for some reason, usually the primary controller must also be retuned. Alternatively, Lee et al. (1998) have developed a tuning method based on Direct Synthesis where both loops are tuned simultaneously. When there are limits on either controller (saturation constraints), Brosilow and Joseph (2002) have recommended design modifications based on the Internal Model Control (IMC) approach. 

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