Metex 2200C Conductivity Analyzer/Controller - Manual (Page 10)

Model 2200C Page 8
4.2 Calibration
4.2.1 All conductivity systems need to be calibrated when first placed in service and
thereafter from time to time. The frequency of calibration can only be found by the
operator’s experience with each process. Calibration must always be performed
when a new sensor is placed in service.
4.2.2 Calibration is accomplished by using buffer solutions, of known conductivity, and
adjusting the instrument to show the known value. Buffers are available in 500 mL
bottles and in 20 L packs from AquaMetrix. The procedure for performing
calibration is very simple and is given in Sections 5.2.
4.3 Temperature Compensation
4.3.1 Temperature compensation is an essential component of conductivity
measuring instruments. Specific conductivity increases with temperature even
though there has been no addition of dissolved solids. It is therefore the industry
standard to compensate for temperature change as if the temperature were
constant at 25°C. The 2200C compensates for a 2% increase in specific
conductivity per °C.
4.4 Relay Outputs
4.4.1 Two SPDT (Single Pole Double Throw) relays are provided. The normally open
contacts, NO, are open when no alarm or control is active.
4.4.2 The control relay can be programmed to close on either rising or falling conductivity.
It is normally used to control a valve, pump or auxiliary device. It may be set to
close at any point on the scale. The deadband, sometimes termed hysteresis,
defines the point at which the relays open.
4.4.3 Refer to Sections 5.4, to 5.6.
4.4.4 The second relay functions as a high-low alarm. It has two programmable
Setpoints (high and low). The deadband is fixed at 2% of full span. The alarm
contact can be programmed to also signal memory loss in the controller. See
Sections 4.7, 5.7, and 5.8.
4.4.5 All relays can be programmed for "fail-safe" operation which reverses the normal
operation of the relay. In fail safe mode the Normally Closed contact functions as
the Normally Open contact. In the event of power loss to the unit, the relay will de-
energize and the device connected to the Normally closed contact will be turned on.
This option is selected with the DIP switches on the swing out board. See Section
4.7.