Some questions regarding the Rosemount 3051CD differential pressure transmitter
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Hello, experts on this forum. I have recently purchased a Rosemount 3051CD differential pressure transmitter to use together with a pitot tube in order to measure the fluid velocity in a bubble column. I have a few questions that I would like you to help me answer: 1. Regarding the measurement range: The designed range is from -6.22 kPa to 6.22 kPa, but my engineer told me that the minimum value that can be measured is 0.12 kPa. The specifications also indicate a minimum range of 0.12 kPa. Does this mean that the range from -6.22 kPa to 0.12 kPa cannot be measured? I really don’t understand. 2. Regarding the connection methods for the high-pressure and low-pressure sides: The engineer told me that the high-pressure side should be connected to the side of the pitot tube that measures total pressure, while the low-pressure side should be connected to the side that measures static pressure. I can understand this. But in my bubble system, backflow occurs, which means the high-pressure and low-pressure sides are reversed, right? What impact does this have on the measurement at this time? Can a negative pressure value occur? So, based on the first question, does that mean it’s impossible to make a measurement at this point? 3. Accuracy issue: The engineer told me that the accuracy is fixed, at only ±0.075% of the range ； But the specification on the sample states that the accuracy is ±0.1% of the range; when the range is less than 15:1, it is ±0.025 + 0.005*(upper limit of range/range)% of the range. Which statement is correct? And what does “range less than 15:1” mean later on? 3. Range adjustment and 4-20mA output: The engineer told me that the range is fixed (i.e., -6.22~6.22 kPa), and it cannot be changed manually unless a Hart communicator is used. My transmitter is connected to an Advantech data acquisition card. So, if I want to change the range to -4~4 kPa, can I do this by modifying the parameters through the data acquisition card? Also, what is the range corresponding to the 4-20mA output? Which pressure values correspond to 4 mA and 20 mA respectively? I hope everyone can help and provide an answer. Thank you!
Personal understanding: 1. The designed measurement range (not the scale range, which refers to the difference between the upper and lower limits of measurement) is from -6.22 kPa to 6.22 kPa; in other words, the lowest value that can be measured is -6.22 kPa, while the highest value that can be measured is 0.12 kPa. All values within this range can be measured. However, all transmitters have a range ratio, which is the ratio of the maximum measurement range to the minimum measurement range. The minimum measurement range is a fundamental parameter of the transmitter; accuracy cannot be guaranteed below this range. 2. Regarding this issue, in my opinion, if there is backflow, the measurements will be inaccurate. 3. The accuracy grades of commonly used transmitters include 0.1, 0.2, 0.5, 0.05, etc. “Range less than 15:1” refers to the ratio of the maximum measurement range to the minimum measurement range, that is, the range ratio. For example, if the maximum measurement range is 0–150 kPa and the minimum measurement range is 0–10 kPa, then their range ratio is 15:1. 3. Whether parameters can be modified through a data acquisition card depends on the user manual or operating instructions. The measurement range corresponding to a 4-20mA output is the actual measurement range of the transmitter. For example, if the transmitter’s actual measurement range is 0~100 kPa, then 4 mA corresponds to 0 kPa, 12 mA corresponds to 50 kPa, and 20 mA corresponds to 100 kPa.....
1. I’m not quite sure what you mean by “minimum measurable value of -6.22 kPa, maximum measurable value of 0.12 kPa” So what does this 6.22 kPa represent? Could you give a detailed explanation? Thank you! The parameters in the figure are those of the sample; mine are in the range of 1 to 2. How are the maximum and minimum measurement ranges defined, as you mentioned? Did I define it myself? Is it necessary to modify the parameters of the differential pressure transmitter to achieve the maximum and minimum measurement ranges? 3. Does the actual measurement range refer to the range that I define myself within the limits permitted by the differential pressure transmitter’s accuracy? Could you please provide a more detailed explanation? Thank you!
In simple terms, pressure changes of less than 0.12 kPa cannot be detected, or the accuracy does not meet the required standards. 6.22 kPa is the maximum detection pressure of the transmitter; exceeding this value results in over-limit conditions or significant accuracy errors.
As a supplementary note, the 0.12 kPa I mentioned refers to the range of pressure difference changes. For example: ranges such as -6.22 kPa to 0.12 kPa, or 0 to 0.12 kPa are all acceptable. If the pressure difference between high and low pressure is less than 0.12 kPa, inaccurate readings will occur.
Use the Huayan data acquisition card to modify the transmitter range. Does Huayan support the Hard communication protocol? If supported, the range can be set. As I recall, the transmitter housing includes mechanisms for manual adjustment of the range limits. After connecting the high and low pressure pipes to the transmitter, (if the transmitter has a digital or analog display, this can be observed directly; otherwise, a resistor should be connected and then an oscilloscope used to measure the current) use a pressure pump to set the lower limit at -4 KPa. Adjust the transmitter’s current output knob until 4 mA is displayed. Then, apply 4 KPa of pressure and adjust the current to 20 mA – this completes the setup. Using the handheld operator, it is possible to directly set the range and read various parameters of the transmitter!
Hello, the engineer told me that the actual range of this transmitter is only 0–6.22 kPa; the range from -6.22 kPa to 0 represents a reversal of high and low pressures, meaning the absolute value of the range is approximately 6.22 kPa. In your example, it’s 0–0.12 kPa; so the difference between high and low pressure is less than 0.12 kPa, right? I still don’t understand what this means here? There is also the range of data collection; the engineer told me that 4 mA corresponds to 0 kPa, and 20 mA corresponds to 6.22 kPa. I connected a 250Ω precision resistor in series after the converter; this means that 1V corresponds to 0 kPa and 5V corresponds to 6.22 kPa. So how can I convert the voltage signal into a pressure difference signal for display? Thank you!