Sensor Installation Handbook Preface 3rd edition - Siemens ...

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Principles of operation 62 Time constant of measuring sensors in liquids For measuring or acquiring medium temperatures in piping systems, sensors are usually installed with protection pockets. These pockets represent the first delay element in the measuring process, the air gap between pocket and sensing element the second. The third delay element is the sensor’s time constant. Of these three delays in series, that of the air gap between pocket and sensing element is the greatest since the heat conductivity of air is poor. This poor transmission of heat from the medium to the sensing element can be considerably improved by filling the air gap with oil or glycerin. If glycerin is used, the welded protection pocket must be inclined. Transfer with time constant = T No sensors transmit the change in a measured variable instantaneously. The delay in transmission time (the time constant, or “lag”, T) can be shown in diagrammatic form. Change in measured variable Time constant T The time taken to transmit 63% of the total change in the measured variable is referred to as the time constant, T. It takes a period equivalent to five times the time constant to transmit approximately 99% of the change in measured variable.
Example of response characteristic Contact fluid Sensor in pipe Output signals The sensor converts the measured variable into an output signal. Sensors (measuring devices) are divided on the basis of their output signals into two main categories: Switching devices, examples: Thermostats, hygrostats, pressure switches Sensor in water without immersion pocket 63 % 1,6 sec Sensor in immersion pocket with contact fluid 63 % 16 sec Sensor in immersion pocket without contact fluid 60 sec Stepless (continuously variable) signals, examples: Temperature sensors, humidity sensors, pressure sensors 63 % Principles of operation 63
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Sensor Installation Handbook Prefac
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Sensor Installation Handbook Prefac
Page 9 and 10:
General notes for all sensors Alway
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Always allow a sufficient length of
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Temperature Immersion sensors · Wa
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Water-resistant seal Chilled water
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If the active length (a) of the sen
Page 19 and 20: Sensors mounted without immersion p
Page 21 and 22: Temperature Probe sensors · Air En
Page 23 and 24: The ambient temperature at the devi
Page 25 and 26: Temperature Averaging sensors Allow
Page 27 and 28: Do not bend the capillary too tight
Page 29 and 30: When installing on "drawer"-type un
Page 31 and 32: Use spacing clips to maintain a 50
Page 33 and 34: Do not install on external walls. A
Page 35 and 36: Temperature Outdoor sensors The sys
Page 37 and 38: Seal gaps between cable/plastic tub
Page 39 and 40: Temperature Surface-mounted strap-o
Page 41 and 42: Temperature Wind sensors Install on
Page 43 and 44: Avoid shade (from trees or neighbou
Page 45 and 46: A test hole must be provided for ev
Page 47 and 48: Distance for adiabatic humidificati
Page 49 and 50: Humidity sensor Average humidity me
Page 51 and 52: Seal gaps between cable/plastic tub
Page 53 and 54: Where there is a risk of condensati
Page 55 and 56: Avoid using tips which protrude int
Page 57 and 58: Where more than one sensor is used,
Page 59 and 60: Pressure Liquids Pressure tapping p
Page 61 and 62: Pressure measurement in conjunction
Page 63 and 64: Flow monitoring Water Correct insta
Page 65 and 66: Avoid recesses (e.g. shelving) and
Page 67 and 68: Floats: These are used in open and
Page 69: Principles of operation General All
Page 73 and 74: Stepless devices Stepless devices (
Page 75 and 76: Bimetal rod and tube Material Const
Page 77 and 78: Electrical resistance sensors Metal
Page 79 and 80: Thermocouples These consist of two
Page 81 and 82: Absolute humidity x g H 2O per kg o
Page 83 and 84: Electronic systems Piezoelectric el
Page 85 and 86: Measuring water velocity and flow L
Page 87 and 88: Room temperature measurement Room s
Page 89 and 90: Calibration of measuring sensors Th
Page 91 and 92: Practical tips Frost protection the
Page 93 and 94: Preventive frost protection thermos
Page 95 and 96: Pressure control in VAV systems The
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