Thermal resistance and PID control in temperature control system of joint action

Where should I find the control system of heat resistance?

used in temperature control system of the thermal resistance should always be as close to need to adjust the temperature closely load or area. Ideally, the thermal resistor should be placed on to control point.

when under control of the thermal resistance and load any distance apart, the temperature change of the load to reach thermal resistance takes time. During this period, the control system has no chance to know anything about change, so you can't adjust.

although the correct adjustment of PID control can try to compensate the thermal resistance between the load and heat isolation, but the results will not be temperature thermal resistance and the load has a tight coupling between system quickly and accurately.

I was beating temperature near the set point. How to reduce this?

above and below the set value of excessive temperature drift is usually below the result of one or more conditions:

a) The distance between the heat resistance and load far

b) Is higher than load the required power of the heater power

c) Bandwidth is too small and/or reset factor is too large, PID control)

d) Lag or dead zone is too high ( ON/OFF control)

I am using PID control. Use the ON/OFF can get the same results?

in general, if your system from the heat source (fast From the change of heater power to observe the temperature change of the load) Move the heat to the controlled area or available heat, matches or exceeds the quantity of heat that use up less than than a factor of about 2, the ON/OFF control will give better performance. That is to say, ON/OFF control will generate less than PID control overshoot, faster and smaller deviation of preheating, without the need for a lot of adjustments.

if there is a long delay, the change between the heater power and the temperature of the load produced many seconds or minutes, or if the heater power over load demand is about 2 times or more, the PID control.

I use mechanical or light bulbs and capillary thermostat. Why do you want to go to the electronic control?

the typical mechanical thermostat will be 5 degrees or more dead zone ( Lag) , sometimes in low cost version reached as high as 20 degrees. Light bulbs and capillary control a bit better, but only a few degrees. This may result in the same amount of fluctuations in temperature control. The absolute precision of mechanical thermostat set-point usually with dead zone about the same, that is, from + / - 5 to 20 degrees.

the temperature stability and precision of electronic controller can be about 10 times, perhaps is four times the size of the cost. If the existing mechanical thermostat performance reduce your process or alarm performance, electronic control could be well worth the extra cost.

I can in the same electronic controller in the process of control I have temperature alarm?

though technically possible, or even a simple, but in the control process of the same electronic circuit configuration within the upper or the temperature alarm is a good idea. Limit or alarm designed to detect a variety of different types of system failure, including electronic circuit fault itself. If you use the same alarm circuit implementation, is impossible to detect all possible failure.

even if it will be more expensive to some extent, careful system design shows that limit and overtemperature alarm and control electronics on electrical and physical separation.

I have more accurate temperature control?

to distinguish between precision and accuracy is very important. （ Please refer to explain the differences between the FAQ section. ）

the precision of temperature control can be specified directly and buy. Temperature control on the readout and the value of precision is usually 1 or 0. 1 degree. The accuracy is a problem of control specification and design.

on the other hand, the precision of temperature control is only part of the specifications and design control itself. Or in according to the international standard calibration accuracy within the limits of maintaining a controlled temperature depends on many factors, such as: control the accuracy of the thermal resistance of the calibration and control of calibration and the stability of the controlled system.

the precision of the temperature in the controlled system can't fully guarantee by the specification of the temperature control itself. It can only be achieved through pay attention to all of these factors.

assume control be specified and designed for such as 0. The accuracy of 1 degree, and the thermal resistance and control has been calibrated to the same figure, and it has been carefully designed thermal system, the heat resistance, has a tight coupling between heater and load matching, then the temperature control accuracy to + / - 1 degree would be very good. Any better should be considered as laboratory level.

if thermal resistance fault, my system will happen?

the correct design of temperature control in the temperature thermal resistance fault broken or cut off the heat when short circuit ( Or cooling) 。

the possibility of a related, it is not clear, should be dealt with in the context of a specific system design. This is the separation of thermal resistance from the controlled area, such as the temperature probe from the hot well.

the fault may be difficult to detect, but can be by a specific circuit or software to solve in the custom design of the control.

I can put my controller with the contactor in the shell?

any electromagnetic or electronic control in some degree will be vulnerable to radio frequency interference. Immune will depend on the control design and packaging; The greater the immunity, the greater the cost, the greater the size usually.

as a general guideline, open electronic controller should not be placed in more than 1 amp contactor switch feet, unless the controller or contactor surrounded in the steel box alone. At the same time, the wire into the controller should be good isolation with the contactor.