Omega CL526 User Manual
17
4.11
Resistance and Rtd simulation
CL526
portable calibrator is equipped with an electronic circuit for the active simulation of platinum and nickel resistance
thermometers and resistances.
It is based on the assumption that the instrument to be calibrated will supply the excitation current to the sensor; this
current must be between 0.2 and 5 mA ( typical working values ).
A lower value will generate an insufficient precision level and a higher current won’t permit the simulation of high
resistance values ( maximum voltage drop on the simulated resistance is 2 V ).
The excitation current must be applied to the pertinent terminals as indicated in par. 7.1 (simulation).
That current, flowing through resistance “ Ra“ (precision ± 0.01%) will generate a voltage drop that will be amplified and
sent to the D/A converter. The output amplifier will simulate the variation of the output resistance as a function of the
value set by the operator through the keyboard.
The connection between “+” and “-” terminals must be left open.
It is based on the assumption that the instrument to be calibrated will supply the excitation current to the sensor; this
current must be between 0.2 and 5 mA ( typical working values ).
A lower value will generate an insufficient precision level and a higher current won’t permit the simulation of high
resistance values ( maximum voltage drop on the simulated resistance is 2 V ).
The excitation current must be applied to the pertinent terminals as indicated in par. 7.1 (simulation).
That current, flowing through resistance “ Ra“ (precision ± 0.01%) will generate a voltage drop that will be amplified and
sent to the D/A converter. The output amplifier will simulate the variation of the output resistance as a function of the
value set by the operator through the keyboard.
The connection between “+” and “-” terminals must be left open.
P
D/A
Keyboard
µ
Set
Out
Ref
Ouput amplifier
Ra
Instrument
to be
calibrated
Input amplifier
4.12
Thermocouples input-output circuit
A thermocouple, a temperature sensor, in its most common form consists of two wires of different composition, joined
together at one end. The two wires are joined together at two points which have different temperatures.
together at one end. The two wires are joined together at two points which have different temperatures.
Measuring junction
Tc wires
Copper wires
emf
output
Reference Junction
The reference junction is also often, but less preferably, called the “cold” junction.
The temperature of the reference junction can be held constant or its variation electrically compensated in the
associated measuring instrumentation.
The second junction is the measuring junction (or “hot” junction).
A thermocouple is a practical tool for temperature sensing because it generates a measurable electrical signal.
The signal is proportional to the temperature difference between the measuring and reference junctions and is defined,
by means of tables, based on the International Practical Temperature Scales (IPTS68 or ITS90).
The portable calibrator CL526 has the reference junction located in the negative (black) terminal post. To improve
overall accuracy the terminals are designed with a very low thermal capacity.
Inside the body of the negative terminal is placed a thin film Pt100 resistance thermometer that dynamically measures,
with high accuracy, the temperature of the reference junction.
The microprocessor uses the above signal (Pt100) to adjust the input signal to compensate for the Rj temperature.
Reference junction compensation can be internal or external, depending upon the application requirements.
The temperature of the reference junction can be held constant or its variation electrically compensated in the
associated measuring instrumentation.
The second junction is the measuring junction (or “hot” junction).
A thermocouple is a practical tool for temperature sensing because it generates a measurable electrical signal.
The signal is proportional to the temperature difference between the measuring and reference junctions and is defined,
by means of tables, based on the International Practical Temperature Scales (IPTS68 or ITS90).
The portable calibrator CL526 has the reference junction located in the negative (black) terminal post. To improve
overall accuracy the terminals are designed with a very low thermal capacity.
Inside the body of the negative terminal is placed a thin film Pt100 resistance thermometer that dynamically measures,
with high accuracy, the temperature of the reference junction.
The microprocessor uses the above signal (Pt100) to adjust the input signal to compensate for the Rj temperature.
Reference junction compensation can be internal or external, depending upon the application requirements.