Level gauge
Thread Content
There are light oil tanks at the site, and it is necessary to measure the level interface between the light oil and the wastewater. The value L is 800 mm; the density of water is 1.0 kg/cm3, the density of oil is 0.9 kg/cm3, and the density of silicone oil is 0.95 kg/cm3. The transmitter supplied by the design institute has a range of 0–7.84 kPa. Based on calculations, the actual range should be –0.394 to –0.390 kPa. After adjusting the gauge’s range, it reads –0.274 kPa. The current supplied to the transmitter is either 19.375 mA or 3.66 mA, and this value does not change regardless of the measurement values or range adjustments. When the connection to the drainage system is disconnected, the gauge reads –7.8 kPa with a current of around 20 mA; after reconnecting the wire, it reads 4 mA, and an alarm is triggered indicating that the range is incorrect. Could an expert please advise on how to resolve this situation?
This post was last edited by sdlyml on 2021-9-9 10:02. I made a mistake; I’ve deleted it
1. The range should be 7.056~7.84 kPa (7.056 kPa = 4 mA = 0%; 7.84 kPa = 20 mA = 100%). As the additional pressure generated by the capillary causes migration, the upper and lower limits of the range change accordingly, while the range itself remains unchanged. 2. Several factors that affect the accuracy of measurement results: First, the upper edge of the flange must be submerged in liquid ； Second, the aforementioned range is too small for double flange connections (less than 1 kPa), resulting in large fluctuations in the measurement values. It is recommended to use other types of instruments, such as floats, radio frequency admittance, or radar (if the dielectric constant is suitable).
The 3rd floor is the correct answer; the differential pressure is too low, and even the slightest change in differential pressure can cause significant fluctuations at the interface. So double flanges are not suitable here.
Ugh, then using a differential pressure transmitter doesn’t work either. I wonder how the level of the reflux tank is measured in the factories where our fellow sailors work
Migration occurs according to the density of silicone oil
If a differential pressure transmitter is used directly, what should be used to measure the medium in a pipeline with negative pressure?
This post was last edited by liu530014416 on 2021-9-11 09:03. The range of the transmitter supplied by the design institute is 0–7.84 kPa; after calculations, the actual range turns out to be –0.394––0.390 kPa. After adjusting the range of the gauge, it reads –0.274 kPa. When the transmitter’s range is set to 0–0.784 kPa, the calculated range is still –0.394––0.390 kPa (which is correct); again, after adjusting the gauge’s range, it reads –0.274 kPa. The current corresponding to –0.274 kPa should be 6.5 mA, but the actual current is not correct. After disconnecting the root for sewage discharge, the measured value was -7.8 kPa with a current of around 20 mA; after reconnecting the wire, the value was 4 mA. Everything was emptied; the pressure reading was correct, and 20 mA was outputted. However, the current value was incorrect. After reconnecting the wire, 4 mA was displayed, which suggests that the gauge is damaged. I’m not sure if it’s a new gauge, but EJAs rarely have problems. 1. Try powering it using the instrument cable nearby. 2. Reset it to factory settings. It’s very likely that the gauge is broken.
This post was last edited by liu530014416 on 2021-9-11 09:07. The interface can be measured using guided-wave radar, ROSEMOUNT 5300
Experts, can a double-flange design have a side interface? Explain it to me – how do you know how deep the water is and how deep the oil is?