Zero drift means that under specified test conditions, when input pressure is zero, the output value jumps forward，negative or up and dowm with time over the specified index. In order to prevent moisture, rain and harmful gases, the transmitter’s circuit board is designed and manufactured in a sealed structure. If the case is not tightened and the hexagonal lock nut is tightened, it will damage the normal working conditions of electronic circuit, and it will be invaded by moisture, rain and harmful gases, resulting in decreased insulation performance or corrosion of electronic components, resulting transmitter output value draft. unstable transmitter output values will directly affect the measurement and control system.
But some zero change are allowed. such as：the change of the zero output value caused by the difference between the installation position of the transmitter and the adjustment position; the diaphragm is perpendicular to the ground when the meter is being calibrated, but when the field is installed, the measuring diaphragm is parallel to the ground or inclined to the ground. It is a normal phenomenon that the self-weight of the sheet causes the zero point change caused by the deviation of the diaphragm from the center position. The smaller the measurement range of the transmitter, the larger the change value. Simply change the zero output value back to zero by zeroing the zero position.
The change in output value due to changes in the ambient temperature of the transmitter is called the temperature additional error of the transmitter. Any change in value that meets the technical specifications is a normal change. The temperature index given in the transmitter’s instruction manual refers to the high range. When calculating the adjusted range temperature index, you need to multiply this indicator by the span ratio (the ratio of the highest range to the adjusted range), the model and specifications of the transmitter. Different, the temperature indicators are also different. In the use of the site early, middle and late output value changes within the scope of the indicator, it should be a normal zero point regular change, this change is particularly obvious in the field with a large temperature difference, the transmitter with a lower range, as long as it does not exceed The indicator is also normal.
It is also a normal change that the static pressure causes the output change in accordance with the technical specifications. Especially for small-range transmitters, due to the large conversion magnification, the output value caused by static pressure changes greatly. The key is to see if there is any technical index.
Post time: Jul-09-2019