Tempco TEC-2500, Инструкция по эксплуатации

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2–5 Sensor Installation Guidelines
Proper sensor installation can eliminate many problems in a
control system. The probe should be placed so that it can
detect any temperature change with minimal thermal lag. In
a process that requires fairly constant heat output, the
probe should be placed close to the heater. In a process
where the heat demand is variable, the probe should be
close to the work area. Some experiments with probe
location are often required to find the optimum position.
In a liquid process, the addition of a stirrer will help eliminate
thermal lag. Since a thermocouple is basically a point
measuring device, placing more than one thermocouple in
parallel can provide an average temperature readout and
produce better results in most air-heated processes.
The proper sensor type is also a very important factor in
obtaining precise measurements. The sensor must have the
correct temperature range to meet the process
requirements. In special processes, the sensor might have
additional requirements such as leak-proof, anti-vibration,
antiseptic, etc.
Standard sensor limits of error are ±4°F (±2°C) or 0.75%
of sensed temperature (half that for special) plus drift
caused by improper protection or an over-temperature
occurrence. This error is far greater than controller error
and cannot be corrected on the sensor except by proper
selection and replacement.
2–6 Thermocouple Input Wiring
The color codes used on the thermocouple extension leads are shown in Table 2.1.
+ +
11
22
33
44
O
N
O
N
1 2 3 4 5
8 9 10 11
6 7
12 13 14
Figure 2.5 Thermocouple Input Wiring
DIP Switch
The thermocouple input connections are shown in figure
2.5. The correct type of thermocouple extension lead-wire
or compensating cable must be used for the entire distance
between the controller and the thermocouple, ensuring that
the correct polarity is maintained throughout. Joints in the
cable should be avoided, if possible.
If the length of the thermocouple plus the extension wire is
too long, it may affect the temperature measurement. A 400
ohms K type or a 500 ohms J type thermocouple lead
resistance will produce approximately 1°C temperature
error.
Thermocouple Cable British American German French
Type Material BS ASTM DIN NFE
Copper (Cu)
+ white + blue + red + yellow
T
Constantan (Cu-Ni)
– blue – red – brown – blue
* blue * blue * brown * blue
Iron (Fe)
+ yellow + white + red + yellow
J
Constantan (Cu-Ni)
– blue – red – blue – black
* black * black * blue * black
Nickel-Chromium
+ brown + yellow + red + yellow
K (Ni-Cr)
– blue – red – green – purple
Nickel-Aluminum
* red * yellow * green * yellow
(Ni-Al)
R Pt-13%Rh, Pt
+ white + black + red + yellow
S Pt-10%Rh, Pt
– blue – red – white – green
* green * green * white * green
Pt-30%Rh
Use + grey + red Use
B
Pt-6%Rh
Copper – red – grey Copper
Wire * grey * grey Wire
Table 2.1 Thermocouple Cable Color Codes
* Color of overall sheath