Charmeg MP-R Installer Manual

The directions given on this sheet concern the following products:
• MR-R
• MP-A
• MP-SW
• MP-N
• MP-F
• MP-T
• MP-TM
In all the above products apart of the temperature set-point which is explained in the respective User's Manuals, some
additional operational parameters can be modified.
A. the Differential
B. the Offset
C. the Upper and Lower Adjusting Limits
D. the Maximum Allowed Floor Temperature (only for MP-F)
The meaning of each of them as well as the step by step process of modifying those parameters is explained below.
ATTENTION
The modifications must be performed always from experienced and officially registered personnel. No end user
should try to perform this modification. The necessity of parameter change from a pre stored value as well as the
consequences to the system are fall in to the exclusive liability of the installer engineer. Charmeg has no liability for
possible damage might be induced as a result of inappropriate or wrong parameter modification. Do not hesitate to
consult Charmeg in case of any misunderstanding.
Parameter Content
Differential is the minimum detected temperature change that is necessary for a thermostat in order to toggle its output
state. Consider for example a room thermostat adjusted at 20°C. Assume the environmental temperature at 15°C. The
thermostat tries to maintain the desired temperature as perfect as it can. When the room temperature reach the predefined
20°C set point the thermostat deactivates the heating system. The room temperature normally overshoots slightly above the
20°C and then decreases rapidly. The set point value minus the temperature point in which the thermostat will activate again
the heating system defines the differential. Because the desired temperature is higher than the heating demand temperature
we trend to say that the differential considered negative. In such a case the room thermostat could have a differential of –
0.6°C. Consequently the room temperature should drop 0.6°C below the 20°C in order to allow the thermostat to reactivate the
heating system. The system will be activated again at 19.4°C. The smaller the operating differential the more precise the
temperature control. In the above example the closest to 20°C the room temperature will be. Indeed in reality some additional
factors interfere the control process and the absolute control remains unreachable. Moreover the small differential can cause
more frequent cycles to the burner of the heating system resulting huge wear out. Tiny differentials should be avoided. In
practice values from –0.6°C to -0.8°C have good results in home and office installations.
Offset is the parameter that adds or subtracts a constant value from the temperature read by the thermostat in order the
final temperature to be closer to the real one. If for example the thermostat displays wrongly 17.5°C while the correct is 18°C
we can rationally conclude that there is an error of -0.5°C. The offset parameter adds this missed 0.5°C to the measurement.
The result is a corrected and accurate temperature reading. Exactly the opposite should be done in case of bigger measured
temperature. If the thermostat displays 18.8°C an offset of 0.8°C should be subtracted from the reading. Generally speaking
the offset value is applied to eliminate the small measuring constant errors they can be present in massive production devices.
Another useful case is when the thermostat has been wrongly installed near to any source (lights, heat radiator) or sink
(window, openings etc) of heat and due to the influence of the source shows incorrect reading. In those cases offset capability
gains crucial importance.
Digital Thermostats MP Series
Installer's Manual
You should be aware of the offset modification. Any possible change must be done carefully. It is considered ineffectual trying
to extinguish differences as low as +/-0.5°C. Particularly room thermostats are not measuring instruments. They include
temperature displays in order to inform the inhabitants for the present room air temperature with a limited degree of accuracy.
Because of the tolerances of the used electronic devices, the inappropriate places of installation as well as other reasons
render thermostat to be susceptible to various parameters which affects accuracy. If somebody would try to comprise a
perfectly measuring device will not unlikely result to double its cost. The most important is to have an indication of the
temperature and gather the information regarding the degree of comfort. If the inhabitants feel good when the thermostat
shows 20°C it is worthless to reveal that the real temperature is slightly above or below 20°C. The modification of the offset
must be performed for the temperature point in which thermostat is to be operated most of the time. For a heating room
thermostat this point is about 22°C. If the working point in unknown use the middle of the adjusting range. For the MP-R this is
(35°C-5°C)/2+5=20°C.
Upper and Lower Adjusting Limits The members of MP series are able to control the temperature among the limits
described in those manuals. It is although very common a tightest adjusting range to be necessary in order to protect the
premises or even the users. For example in thermostats installed in the rooms of a hotel a narrower range might be more
preferable.
Maximum Allowed Floor Temperature (only for MP-F) In under floor designated thermostats an additional feature is
unexceptional. The device measures also the floor temperature and takes track to be always under a predefined limit (usually
45°C). If the temperature exceeds this limit the thermostat interrupts the heat demand signal protecting the overall under floor
piping from overheating. The floor maximum temperature can be trimmed in MP-F.
Parameter Modification
In the following table directions for the necessary actions in case of parameter modification can be found. Inside the
parentheses are the factory pre stored values.
Differential
ΟΝ ΟΝ
27 Kotronos str. Aegaleo- Athens- Greece
Tel.+30 210 5693111 Fax +30 210 5693093, www.charmeg.gr
Maximum T emperature Τ max
°C
Desired T emperat ure 20
Minimum T emperature Τmin
ΟΝ
Burner
Time t
Doc. No: Installers_manual_MP_gr_en_3.doc