External Digital Encoder
As a standard, Yokogawa pressure transmitters have external digital encoders that allow for adjustment of the zero-point.
Differential Pressure Transmitters
Before adjusting the zero point, make sure that the equalizing valve is open. The zero-adjustment screw is located inside the cover. Use a slotted screwdriver to turn the zero-adjustment screw. Equalize the transmitter, then turn the screw clockwise to increase the output or counterclockwise to decrease the output. The zero point adjustment can be made with a resolution of 0.01% of the setting range. The degree of zero adjustments varies with the screw turning speed; turn the screw slowly to make a fine adjustment, quickly to make a rough adjustment.
Gauge / Absolute Pressure Transmitters
When you can obtain the Low Range Value from the actual measured value of 0% (0 kPa, atmospheric pressure)
For pressure measurement using gauge pressure transmitters, follow the steps below before performing the zero-point adjustment.
- Close the tap valve (main valve).
- Loosen the fill plug so that the pressure applied to the transmitter is only the head of the seal liquid.
- Adjust the zero point at this point.
- After the adjustment, close the fill plug and then gradually open the tap valve.
Use a slotted screwdriver to turn the zero-adjustment screw. Turn the screw clockwise to increase the output or counterclockwise to decrease the output. The zero point adjustment can be made with a resolution of 0.01% of the setting range. Since the degree of the zero adjustments varies with the screw turning speed, turn the screw slowly to make a fine adjustment and quickly to make a rough adjustment.
When you cannot obtain the Low Range Value from the actual measured value of 0%
Adjust the transmitter output to the actual measured value obtained by a digital manometer or a glass gauge.
[Example]
The measuring range of 50 to 250 kPa; the actual measured value of 130 kPa
Turn the screw to match the output signal to the actual measured value.
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