Mettler Toledo M400/2(X)H Especificaciones descargar pdf (Pagina 70)

Transmitter M400/2(X)H, M400G/2XH 70

Printed in Switzerland 30 031 683

10 PID setup

(PATH: Menu / PID Setup)

PID Setup

Tune

Parameters

ModePID A/M

PID Display

Setup

PID control is proportional, integral and derivative control action that can provide smooth regula-

tion of a process. Before configuring the transmitter, the following process characteristics must

be identified.

Identify the control direction of the process

– Conductivity:

Dilution – direct acting where increasing measurement produces increasing control output

such as controlling the feed of low conductivity diluting water to rinse tanks, cooling towers

or boilers

Concentrating – reverse acting where increasing measurement produces decreasing control

output, such as controlling chemical feed to attain a desired concentration

– Dissolved Oxygen:

Deaeration – direct acting where increasing DO concentration produces increasing control out-

put such as controlling the feed of a reducing agent to remove oxygen from boiler feedwater

Aeration – reverse acting where increasing DO concentration produces decreasing control

output, such as controlling an aerator blower speed to maintain a desired DO concentration

in fermentation or wastewater treatment

– pH / ORP:

Acid feed only – direct acting where increasing pH produces increasing control output, also

for ORP reducing reagent feed

Base feed only – reverse acting where increasing pH produces decreasing control output,

also for ORP oxidizing reagent feed

Both acid and base feed – direct and reverse acting

Identify the control output type based on the control device to be used:

Pulse frequency – used with pulse input metering pump

Pulse length – used with solenoid valve

Analog – used with current input device such as electric drive unit, analog input metering

pump or current-to-pneumatic (I / P) converter for pneumatic control valve

Default control settings provide linear control, which is appropriate for conductivity, dissolved

oxygen. Therefore, when configuring PID for these parameters (or simple pH control) ignore set-

tings of deadband and corner points in the tuning parameter section below. The non-linear con-

trol settings are used for more difficult pH / ORP control situations.

If desired, identify the non-linearity of the pH / ORP process. Improved control can be obtained if

the non-linearity is accommodated with an opposing non-linearity in the controller. A titration

curve (graph of pH or ORP vs. reagent volume) made on a process sample provides the best

information. There is often a very high process gain or sensitivity near the setpoint and decreas-

ing gain further away from the setpoint. To counteract this, the instrument allows for adjustable

non-linear control with settings of a deadband around the setpoint, corner points further out and

proportional limits at the ends of control as shown in the figure below.

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Mettler Toledo M400/2(X)H Especificaciones Pagina 70

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