Technical_reference - 第30页

Technical Service Manual 30 Revision Dat e: August 2004 (FOR FUTURE USE) SHORTED THERM OCOUPLE S YMP TOMS : 1) A Cell indicates an under tem perature condition in which the tem peratur e rises but does not reach s et poi…

Technical Service Manual 29 Revision Date: August 2004

One (or more) Cells is indicating an under temperature condition where the temperature rises, but does

not reach set point. Excessive factory exhaust flow is a possibility.

POSSIBLE CAUSES

If the factory exhaust flow is much too high, then the oven will lose large amounts of heated gas while trying to heat up to

“Process Ready”. Because of this, the oven can only raise the internal temperature to some level lower than the set

point. Throttling the factory exhaust flow will reduce the cooling effect of cold air infiltration to the oven and allow it to

come up to setpoint temperature.

HINT: Check actual exhaust rate and compare it to the recommended exhaust rate in the Site Preparation Manual.

EXCESSIVE AIR ENTERING THE OVEN

One (or more) Cells is indicating an under-temperature condition in which the temperature rises

but does not reach set point. Too much cool air entering the oven is a possibility.

POSSIBLE CAUSES

This condition may be caused two different ways:

1) Incorrect ICB settings. The ICBs must be properly adjusted to bias the airflow correctly on both ends of the oven.

This may mean air coming slightly into the oven at the ends, but not an excessive amount (ICBs can be adjusted to

expel a small amount of air). Whichever setup is selected, it must be correct for the oven and application.

2) Other external sources of cool air are always a possibility. For example, a large fan or room air conditioning blowing

cool air towards the oven opening.

(ICB = Inter Cell Baffle)

LOOSE WIRE

A Cell indicates an under temperature condition where the temperature rises but does not reach set point.

A loose or open conductor supplying electrical power to the heater may cause this condition.

POSSIBLE CAUSES

The heaters all have four connections for AC voltage and ground INSIDE the cell. Any of the four could be loose. The

conductors supplying the heaters run from the circuit breakers to the SSRs, out of the electrical panel, across the 'tops' of

the cells to terminal blocks on the Cells.

If this condition occurred after changing a component, check for captured insulation on wires and terminals. Tighten any

loose connection(s) found, then check the operation of the oven

Technical Service Manual 30 Revision Date: August 2004

(FOR FUTURE USE)

SHORTED THERMOCOUPLE

SYMPTOMS:

1) A Cell indicates an under temperature condition in which the temperature rises but does not reach set point.

2) A Cell indicates an under temperature condition in which the cell appears to stay cold. (The actual temperature

could be very high.)

3) A Cell indicates an under temperature condition. (The Cell temperature was operating at setpoint, but now has

dropped from setpoint.)

POSSIBLE CAUSES

A shorted Thermocouple is a possibility. When a T/C is shorted, the two T/C conductors touch each other (not

intentionally) somewhere between the controller and the T/C sensing tip. The temperature “sensing” occurs at the location

of the “short”, instead of the tip.

The thermocouple is intended to “sense” the temperature at the cell face, so when a T/C shorts, the “indicated

temperature” will be lower than the “actual temperature” at the cell face.

HINT: Check the percent power indicators.

One Cell in the Zone with the shorted T/C should be at 100% power and the opposite Cell should be at 0% power.

One cell will shut off (0%) because the shorted Cell (100%) is causing a high tunnel temperature because of

misinformation received from the shorted T/C.

HINT: When this under temperature condition exists, check all T/C terminations and connectors. A simple check for a

short: remove the T/C connector from the cell and check the percent power indicators to see if the Cell stops overdriving.

(An open T/C should read as 999

C.)

Technical Service Manual 31 Revision Date: August 2004

PHASE FAILURE

A Cell is indicating an under-temperature condition in which the temperature rises but does not reach

set-point. An under voltage condition is a possibility. The under voltage condition can occur when one

phase of the power drops out.

POSSIBLE CAUSES

At lower voltage, the heater will produce less heat. Check the voltage at the Circuit Breakers first. If supply power is O.K.,

then the problem is with the heater or heater conductors. On reduced voltage, the heater may not produce enough heat

to reach set point during start-up.

(Each heater is connected to two phases of the three-phase power)

HINT: Check the heater conductors where they pass through the metal tube on the top of the cell. Remove the heater

plate and check the conductors and connections inside the Cell at the heater’s terminal blocks. Missing a leg could mean

that the circuit breaker for the heater tripped, or it could be a bad connection on the heater panel itself at the terminal

blocks. It could also be a bad connection anywhere in the wiring from the relay board to the heater.

* This could cause both legs to be without power.

GENERAL OVEN FAILURE

There is an under temperature condition where the entire oven appears to stay cold. This condition

is probably the result of a major oven control failure.

POSSIBLE CAUSES

Some reasons for this type of failure might be:

1) The controller fails to activate any heaters. (The AI board may have failed)

2) The 3-phase power turns into single-phase power (loss of 1 power leg) and some heaters will not operate properly.

(Heaters are single phase and with the loss of one phase, depending on which phases supply power to them,

some would operate properly.)

3) The control transformer circuit breaker tripped producing a power loss to all 120 VAC devices

(K2 will de-energize and remove power from the heaters)

POWER LOSS TO HEATER

A Cell indicates an under temperature condition following a drop from set point. This might be a result

of power loss to a heater.

POSSIBLE CAUSES

When the power to a heater is taken away, the heater cannot maintain the heat level that it has attained. The result is the

heat level in that cell dropping from the set point to some lower value. This may also be the result of thermal drift to a

lower temperature section of the oven. If the temperature drop is showing up in a cell which is a boundary cell for a

temperature change, and the heater in one of the lower temperature cells stops working, the thermal drift from high to low

may show up as a drop from set-point in the (normally) higher temperature cell. One possible way to find this failure

would be to disable power to the suspect heater in the software and watch for no change in the symptom. If there is a

change in the symptom, then the heater in question may not be the one that failed.