Metex 2200R ORP Analyzer/Controller - Manual (Page 11)

Model 2200R Page 9
4.2 Calibration
4.2.1 All ORP 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 ORP, and adjusting
the instrument to show the known ORP 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
3.5.1 Temperature compensation is not a requirement for ORP measurements, and
consequently the process temperature is not sensed by the ORP probe. However
the 2200R can be used to monitor temperature and provide a temperature output if
you have ordered an ORP probe fitted with a temperature sensor.
4.4 Relay Outputs
4.4.1 Three SPDT (Single Pole Double Throw) relays are provided. The normally open
contacts, (NO), are open when no alarm or control is active.
3.5.1 The two control relays can be programmed to close on either rising or falling ORP.
They are normally used to control a valve, pump or auxiliary device. They may be
set to close at any point on the scale. The deadband, sometimes termed
hysteresis, defines the point at which the relays open. Refer to Sections 4.7, 5.5 –
5.10.
4.4.3 The third 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 relay can be
programmed to signal memory loss in the controller. Refer to Sections 4.7, 5.11,
and
5.12.
3.5.1 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. Refer to
Section 4.7.
3.5.2 An option provides cycling for Relay A and Relay B to obtain closer process control.
When the process is between the setpoint and deadband the relay will cycle on and
off, based on the cycle times selected by the user. This enables the process to mix
with the chemical being added and reduces overshooting. Refer to Section 5.10.