Walchem W600 Series Instruction Manual page 14

voltage wiring in conduit that is separated a minimum of 6 inches from low voltage DC signal lines (such as the sensor
signal).
The sample loop consists of a shut off valve, a cooling coil or plate, a sensor, an optional pH adapter assembly, a pump,
or any combination thereof. The shut off valve is to quickly isolate the system if necessary. A cooling coil or plate is
necessary to cool the nickel solution down to a temperature acceptable to a sample pump and/or pH electrode (if appli-
cable). Cooling the solution is also recommended to help reduce the amount of plate-out that may form in the sample
loop. The pH adapter assembly is used to mount an in-line pH electrode. It should be mounted such that the electrode is
always immersed in the 'U' trap. The pump may be either a stand-alone sample pump (which will typically have high
temperature restrictions), or a high temperature pump (which is usually a branch off of the recirculation pump).
The flow through sensor/sample loop must be installed according to the following guidelines:
• Mount the sensor on a vibration-free, vertical surface so that the sensor tubing inlet connection is at the bottom and the
outlet is at the top. The vertical orientation will prevent air bubbles from being trapped in the sensor.
• Install a shut-off valve at the beginning of the sample loop so that the system may be shut off quickly if necessary.
• If a sample pump is to be used, it must be installed last, after the cooling coil or cooling plate, the flow through sensor,
and the pH adapter assembly, if applicable.
• If a high temperature recirculation pump is to supply flow, adjust flow rate through the sample loop between 400 - 500
mL/min (approx. 0.11 - 0.13 gal/min). This flow rate will help ensure adequate cooling of the solution while maintain
ing a reasonable lagtime in longer runs of tubing. If this is not possible or is undesirable, see Application Notes below.
Other installation guidelines that may be helpful in the overall system:
• Mount the sensor as close to solution as possible. Keep tubing distances to the sensor inlet as short as possible to avoid
hydraulic lag time. Maximum recommended length of tubing from solution to sensor is 25 feet. If this is not possible,
see Application Notes below.
• The solution inlet should draw sample from an area of good solution movement in order to respond quickly to
chemical additions. However, the solution inlet should not draw too near to where the chemistry is added to avoid
artificial 'spikes' in concentration.
• The solution discharge should be open to atmospheric pressure in order to ensure proper flow.
• The cable connector to the controller is keyed, do not force!
Application Notes
If the distance from the solution to the sensor is further than the recommended length of 25 feet, the maximum lagtime
must be calculated from the desired control band to determine a pump flow rate based on a given distance of standard,
uniform tubing. The maximum lagtime is the maximum allowable time for the solution to continuously get to the sensor
in order to achieve the desired control band.
To calculate maximum lagtime:
Max. Lagtime
where Control band = Maximum deviation of concentration
Depletion rate = Rate at which the bath will deplete per unit of time
The deadband should be adjusted so that it is 1/4 the desired control band.
For Example: The set point is 4.00 g/L.
= Desired Control Band*
4 x Depletion Rate
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