User`s guide

Appendix E – Measuring pH with UMC800 Controller and Durafet II Cap Adapter
Standardization Objective
Release E UMC800 Control Builder User’s Guide 263
1/01
Standardization Objective
Purpose
The purpose of the function blocks attached to the pH analog input block (Figure 75) are to capture the
millivolt values of the pH probe output during the zero and slope standardization operations, a time when
the probe is placed in a known buffer solution.
The temperature of the buffer solution is also captured, but only during the zero standardization operation.
These values are then input into the pH math calculation, along with the on-line probe millivolt and
temperature measurements to determine the actual pH value.
Newstart
In addition to capturing the standardization values, NEWSTART digital signals are used on selected blocks
to pre-load default values for the input measurements. A startup recipe will be used to define these startup
values through Variable entries.
A secondary operation after standardization to transfer the values captured during standardization to the
startup recipe variable values will insure the standardization values will not be lost during configuration
changes.
Analog switch blocks
The Analog Switch (SW) blocks that are connected to the MV Input block and Temperature Input block are
used to replace the MV input and temperature input with default values (Variables) for two seconds on a
controller NEWSTART.
Track and Hold functions
TAHD (Track and Hold) functions capture these values during this time period and retain the values on
their outputs. The Track and Hold block is active for one second during this 2-second period from a one
second pulse from the OR block connected to its track command pin input. This operation pre-loads
default zero, slope and temperature values into the Track and Hold function blocks on a NEWSTART.
The Track and Hold function blocks are also used to capture the values of the buffer solutions used during
the NEWSTART and standardization procedure. These blocks are located directly below ZERO and
SLOPE CAPTURE functions in Figure 75.