Milnor 30015T5E Installationshandbuch PDF herunterladen (Seite 15)

Chapter 1. Commissioning

PELLERIN MILNOR CORPORATION

Supplemental Topic 2

Maximizing Chemical Injection Precision

Injection of a consistent amount of chemical is important in controlling wash quality and

using chemicals economically. When chemicals are injected by units of time, as is done with

most washer-extractors, injections of short duration can be imprecise because of two reasons:

• Fine adjustments to the delivered quantity are not possible. For example, if an injection of

three seconds is extended by one second, the quantity delivered is theoretically increased

by more than 30 percent. However, if an injection of 20 seconds is increased by one

second, the theoretical quantity is increased by only five percent.

• Variations in the time between the start of the chemical signal and the start of the chemical

delivery into the machine can cause significant differences in the quantity of chemical

injected. In this case, if a pump starts more slowly some times than others, or if the

delivery tubes are partially empty at the start of the inject period, the quantity of chemical

delivered may vary significantly. As an example, assume a peristaltic pump moves

chemical along the delivery tube at a rate of three feet per second. If the delivery tube is

empty for three feet along its length, then one second of the injection time is spent injecting

air rather than chemical. If the programmed injection time is only three seconds, then one

third of the desired chemical is not being delivered. However, if the programmed injection

time is 20 seconds, the chemical delivery is only five percent less than desired.

Increasing the programmed injection time makes any variation less significant. Use pumps

and/or valves sized to allow inject times of at least 10 seconds. If injection times for a specific

chemical vary widely from one formula to another, consider using two pumps or valves for the

same chemical. Actuate one pump for injecting small quantities, and use both pumps or valves

for larger quantities.

1.4.1.

Pump Signal Connections

The microprocessor controller used on TxE models closes certain relay contacts when

chemicals are desired and to flush the chemical system after each injection. These signals are 240

volts AC, and cannot be made potential-free. Any device driven by this signal can draw up to 37

milliamperes.

Note 2:

The manifold flush signal is effective only if the chemical supply system (provided by others) is

properly designed and connected to a flushing water source.

Caution 8 : Component Damage Hazard

—Board components will burn out and

require board replacement if devices driven by inject signals do not meet the above

electrical specifications. Pumps generally draw a higher current than specified, and will

cause board damage.

This machine provides signals for three chemicals and a manifold flush. Table 2 contains the

connection details for these signals. All chemical signal connections are available in on terminal

strip TBS, as shown in Figure 4. This terminal strip is located in the electrical enclosure on the

left rear of the machine, where the machine power connections are made.

Note 3:

Unless the “Timer Stop” feature is employed, each chemical signal is enabled for 30 seconds,

starting 15 seconds after the desired level (usually low level) is achieved for the bath.

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