Zero trim
- Thread starter nabi
- Start date
The answer depends on what you mean by "zero trim".
If "zero trim" means a minor adjustment generally due to the installation orientation of the DP transmitter, then yes, any major player, industrial grade PT will have a HART or keypad instruction to trim a minor offset to zero, assuming that the differential pressure on both ports is zero, having been equalized to zero DP by external valving.
If by "zero trim" you mean, "can the transmitter have an LRV of 0.0 instead of -1600mmH2O, and a URV of 1600mm H2O", then it will depend upon brand and model of the PT.
The former Siemens DSIII had a procedure to do that, but its replacement, the P320 does not, because of the safety considerations involved in P320, which is SIL 3 qualified. The safety engineers think that offsets beyond ±10% of the capsule/sensor span are "excessive" in a safety environment and therefore limit the scaling to less than ±10% of span. The digital display can be configured to display whatever range your heart desires, and the 4-20mA output is always interpreted as the range in which it has been defined at the receiver end. But, in terms of the values for LRV and URV there could be limitations on SIL 3 PTs.
If "zero trim" means a minor adjustment generally due to the installation orientation of the DP transmitter, then yes, any major player, industrial grade PT will have a HART or keypad instruction to trim a minor offset to zero, assuming that the differential pressure on both ports is zero, having been equalized to zero DP by external valving.
If by "zero trim" you mean, "can the transmitter have an LRV of 0.0 instead of -1600mmH2O, and a URV of 1600mm H2O", then it will depend upon brand and model of the PT.
The former Siemens DSIII had a procedure to do that, but its replacement, the P320 does not, because of the safety considerations involved in P320, which is SIL 3 qualified. The safety engineers think that offsets beyond ±10% of the capsule/sensor span are "excessive" in a safety environment and therefore limit the scaling to less than ±10% of span. The digital display can be configured to display whatever range your heart desires, and the 4-20mA output is always interpreted as the range in which it has been defined at the receiver end. But, in terms of the values for LRV and URV there could be limitations on SIL 3 PTs.
@David_2
Do you have a source for the +-10% of the span for the siemens P320? i'm looking throught their documentation and there's nothing of use I can find...
Do you have a source for the +-10% of the span for the siemens P320? i'm looking throught their documentation and there's nothing of use I can find...
I view of that as just an example. There is nowhere that they say (Siemens or any other manufactoror that I've been looking at) if the range of the transmitter is 0 - 1 bar, that the maximum preload pressure is 0.1 bar.
My problem was trying to set a Siemens P320 to measure from 0.25 to 1.25 bar with a pressure transmiter with a range of 0 - 1 bar. So I'm looking into what got me to thinking that I can do it. I thought that the span can be 0 - 1 bar but it could be set anywhere in the range of 0 - 6 bar (what the diaphragm could take). For example the 0.25 to 1.25 that I wanted.
Looking at some older documentation some transmitters had range to be larger than span. Now it seems that range is defined with maximum span.
Anyways thanks for your help, I would only appreciate a source or something that says that I can't do what I was planning to do.
My problem was trying to set a Siemens P320 to measure from 0.25 to 1.25 bar with a pressure transmiter with a range of 0 - 1 bar. So I'm looking into what got me to thinking that I can do it. I thought that the span can be 0 - 1 bar but it could be set anywhere in the range of 0 - 6 bar (what the diaphragm could take). For example the 0.25 to 1.25 that I wanted.
Looking at some older documentation some transmitters had range to be larger than span. Now it seems that range is defined with maximum span.
Anyways thanks for your help, I would only appreciate a source or something that says that I can't do what I was planning to do.
Every transmitter has a maximum range that it can measure. You don't something for nothing so you don't get 1.25 bar out of 0-1.0 bar transmitter.
The so-called smart transmitters allow you to range or scale the output to some range smaller than the maximum range of the transmitter, but do not allow you to range or scale the output to a range greater than the maximum range. So you can range your 0-1 bar transmitter 0.25 to 0.75 bar or 0.1 bar to 0.9 bar or whatever range is less than 1.0 bar.
But you can't range a 0-1.0 bar transmitter over 1.0 bar at the top/span end, the URV.
A receiver's AI has to be scaled properly so that 20.0mA represents 1.0 bar, but HMI will let you display the data on a scale going above the transmitter's maximum range with the understanding that there will won't be any valid data points above the transmitter's maximum range. 20.0mA will max out at 1.0 bar but the HMI scale can be 1.25 bar or whatever your heart desires. Do your scaling in the HMI.
The so-called smart transmitters allow you to range or scale the output to some range smaller than the maximum range of the transmitter, but do not allow you to range or scale the output to a range greater than the maximum range. So you can range your 0-1 bar transmitter 0.25 to 0.75 bar or 0.1 bar to 0.9 bar or whatever range is less than 1.0 bar.
But you can't range a 0-1.0 bar transmitter over 1.0 bar at the top/span end, the URV.
A receiver's AI has to be scaled properly so that 20.0mA represents 1.0 bar, but HMI will let you display the data on a scale going above the transmitter's maximum range with the understanding that there will won't be any valid data points above the transmitter's maximum range. 20.0mA will max out at 1.0 bar but the HMI scale can be 1.25 bar or whatever your heart desires. Do your scaling in the HMI.
