Calibration Method Selection - London Electronics EasyReader ER4P Instruction Manual

Calibration Methods
There are two ways you can calibrate your meter. You can type-in theoretical calibration values, or
you can connect the meter to your system and make the meter's readings agree with known
conditions in the system.
1) Calibration without the need for an input signal.
This is known as the 'THEORETICAL' Calibration method
Disconnect the 'calibration mode' terminal from common to enable this method.
If you know the input signal range, and the display values required, you can tell the meter what to
read for two known signal levels. Let's assume that you have a sensor giving 4-20mA for a pres-
sure range of 0 to 250 bar. Select the 'THEORETICAL' calibration switch position on rear of the
meter.
You need to tell the meter what 0% input signal level will be (4mA) and then what 0% reading value
will be (0). Next, you'd tell it what 100% input signal level will be (20mA) and what 100% reading
value will be (250).
2) Calibration when you inject signals into the meter, either from a calibrator or a sensor in
the system.
This is known as the 'DIRECT' calibration method. Signals must be stable.
Connect the 'calibration mode' terminal to common to enable this method.
This can give the best system precision, because you weill use real signals as your reference, and
any errors in the meter or sensor will be allowed for in the calibration process. You need to select
the 'DIRECT' calibration switch position on the rear of the meter.
Apply 0% of signal range. (If the signal comes from a sensor, you don't need to know the value of
signal itself, only what the meter should read at that time. Let's assume you have a pressure
sensor covering 0-250 Bar) Using the buttons on the meter, you'd tell the meter what it should read
now(ie with no pressure applied to the sensor, should read 0).
Now apply 100% of signal range (If the signal comes from a sensor, apply 250 Bar to the sensor or
a lesser known pressure. The accuracy of calibration will be better with higher applied signals).
Using the buttons, you'd adjust for a reading of 250, or the lesser pressure you applied.
A separate, dedicated page covers this calibration method in detail.
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