Temperature alarm

Temperature detectors embedded in the motor winding give close, accurate indication of motor temperature. Both conventional resistance temperature detec tors (RTD) and special thermistors (highly temperature-sensitive nonlinear resistors) are used. With appropriate auxiliaries these devices can indicate or record motor temperature, alarm, and/or shut down the motor. 

Install high temperature alarm, and interlock to activate cooling or shut off feeds at desired temperature... 

Provide high/low temperature alarms to shut off feed... 

The minimum alarms and trips reeommended for eaeh major driver and driven maehine should be a low oil pressure alarm, a low oil pressure trip (at some point lower than the alarm point), a low oil level alarm (reservoir), a high oil filter differential pressure alarm, a high bearing metal temperature alarm, and a metal ehip deteetor. See Table 15-1. 

To simulate the next summer s condition the plant was run at the desired production rate and two cooling tower fans were turned off. It turned out that the cold water temperature rose to slightly above that predicted for the next summer. A thorough inspection of critical temperatures and the plant s operation indicated that the plant would barely make it the next summer. Process side temperatures were at about the maximum desired, with an occasional high oil temperature alarm on the large machines. 

Consider need for high/low temperature alarms for refrigerated storage these should be inspected and tested regularly. Consider need for mitigatory measures (fire, blast, fragment-resistant barricades/screens), electrical and electrostatic safeguards, personal protection, disposal etc. 

Appropriate design features may include feed-forward temperature control, high temperature alarms, high-temperature cutouts to stop feed flow and open a vent to atmospheric or closed system, adequate temperature monitoring through catalyst beds, etc. 

Following some mtxiifications to a pump, an operator pressed the stop button on the control panel and saw that the pump running light went out hence closed a remotely operated valve in the pump delivery line. Several houi s later the high-temperature alarm on the pump sounded soon afterward there was an explosion in the pump... 

Support Systems -fVrKTcdurci . rinil fwni.ihle Lun fiir alJi.-rMii c room cowling on loss of IIVAC I o.pi -Temperature alarm, in mcmi. lo dctc. HVAC(h,p-( - Rcvibc procedures and [raimng lor Jov- c support systems (b,p)... 

Several hours later, the high-temperature alarm on the pump sounded. Because the operator had stopped the pump and seen the Pump Running light go out, he assumed the alami was faulty and ignored it. Soon afterward an explosion occurred in the pump. 

Flare and vent systems should be simple. It is better to avoid water seals than install steam heating systems and low-temperature alarms, which might fail. 

A similar incident occurred on another plant. The liquid in the plant was cold, so a low-temperature alarm was installed in the sump. It was tested with cold water and worked well. When a leak occurred, the leaking liquid, which was acidic, reacted with the steelwork on its way to the sump and warmed up the temperature element could not, of course, tell the difference between warm air and warm liquid and failed to detect the leak. 

Install a high-temperature alarm or trip on the delivery line. 

To prevent similar incidents from happening, if heavy oil is being transfen ed into a tank, incoming oil should be kept below 100°C, and a high-temperature alarm should be installed on the oil line. Alternatively, water should be drained from the tank, the tank kept above 100°C. and the tank contents circulated before the movement of oil into the tank starts. In addition, the movement of oil into the tank should start at a low rate. 

Column temperature alarm Not a complete indication at this stage. It may be a spurious alarm Cross-examine related indicators Data collection Can operator acquire irrelevant or insufficient data Can operator fail to crosscheck for spurious indications Identification/lnterpretation Can operator fail to consider all possible system states and causes of problem Can operator fail to perform a correct evaluation Can operator fixate on the wrong cause Goal Selection Can operator fail to consider possible side-effects Can operator fail to consider alternative goals Can operator fixate on the wrong goal ... 

Heaters and furnaces should also be designed in accordance with standards and codes. Boilers and heating units must be inspected periodically in accordance with codes, insurance requirements and state regulations. Proper controls, interlocks and fail-safe instnunentation must be provided. The heaters should also be provided with sight glasses for flame observation, monitoring devices for flame-out detection, and temperature alarms. 

Consider need for high/low temperature alarms for refrigerated storage these should be inspected and tested regularly. 

A safety trip can be incorporated in a control loop as shown in Figure 5.24a. In this system the high-temperature alarm operates a solenoid valve, releasing the air on the pneumatic activator, closing the valve on high temperature. However, the safe operation of such a system will be dependent on the reliability of the control equipment, and for potentially hazardous situations it is better practice to specify a separate trip system such as that shown in Figure 5.24b. Provision must be made for the periodic checking of the trip system to ensure that the system operates when needed. 

Provision of high-temperature alarms and interlocks to shut down reactor feeds, or heating systems, if the temperature exceeds critical limits. 

More Flow Failure of compressor controls High rate of reaction, high reactor temperature high-temperature alarms (TA1)... 

Cooling water service failure and low flow alarm Install high temperature alarm to alert operator DAC 2/93 ... 

Figure 11-8 Reactor with high-temperature alarm and temperature controller.

If a safety function does not apply, the horizontal line is continued through the safety function without branching. For this example, the upper branch continues through the second function, where the operator notices the high temperature. If the high-temperature alarm operates properly, the operator will already be aware of the high-temperature condition. The sequence description and consequences are indicated on the extreme right-hand side of the event tree. The open circles indicate safe conditions, and the circles with the crosses represent unsafe conditions. 

The event tree for the modified process is shown in Figure 11-11. The additional safety function provides a backup in the event that the high-temperature alarm fails or the operator fails to notice the high temperature. The runaway reaction is now estimated to occur 0.00025 time per year, or once every 400 years. This is a substantial improvement obtained by the addition of a simple redundant shutdown system. 

Monitor material and building temperatures where feasible with high-temperature alarms. 

Temperature indicator (with high-temperature alarm if deemed necessary). 

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