Manual pressure test hydraulics goes digital. How to navigate digital pressure testing.

Traditional borden tube pressure gauge, datalogging digital gauge and pressure transducer. Images by courtesy of WIKA and Hydrotechnik,

After four decades of analogue pressure measurement on our Micropac hydrostatic pressure test pumps, digital is the future for many customers. Digital means different things to different people. 

We are going to look at basic pressure indication using borden tube gauges, data logging using a digital pressure gauge and pulling a pressure reading from a pressure transducer in the system. There is quite a lot to unpack in there. We are equipment manufacturers and not instrumentation engineers who use this kit all the time. Hence, we will have a different take.

Are we talking about replacing our manual test pump with a press button and electric or air driven unit?

No, we aren’t looking at a push button test set for a lot of money. A Micropac manual pressure test pump for water and multiple fluids is still a very cost effective and easy solution. If you want less pumping, look at our DUO unit which will prefill and pressurise to a preset level using a button or knob then use the integral Micropac hand pump to make final adjustments. Lots of professionals still prefer some manual control. The DUO is a great product for plant or site and we have sold a lot of them. Or use the manual Micropac 100% if there is no air on site.

What is a Borden Tube Pressure gauge?

This is the technical description of the bulk of old fashioned legacy pressure gauges. There are also “capsule” gauges for very low pressure, but we have never used one.

Schematic of a borden tube pressure gauge. Image courtesy of Wika

Is an analogue borden tube still a decent alternative to a digital pressure gauge?

We would say yes. Just decide what you actually require. We have always been great fans of old generation borden tube analogue pressure gauges. We still sell a lot of these. We don’t rate cheap and nasty gauges as you really don’t want a failure on a 5 GBP part to cause a 2K test pump to fail. We still use WIKA or Badotherm gauges as our first choice. Also Ashcroft on certain jobs. Ashford Instrumentation have been a chosen supplier for a very long time for our business. Gauges are invariably glycerine filled for damping.

A digital gauge is a great alternative to an analogue gauge, but at a price. We would not use cheap digital gauges. Having tried various makes, the Hydrotechnik units have proved very good for Sarum Hydraulics. Those are supplied on our pumps. There are more features on a digital gauge, so customers would be offered both options. The cost difference often keeps people on the old-fashioned analogue route. Gauges of both types do get broken in service, so replacement cost also needs to be considered.

Is a digital pressure gauge or pressure transducer more accurate than a conventional borden tube pressure gauge?

There is some complication here. This seems like a simple question with a complex answer. We would simply look at the technical data. For example, a class 1 63mm borden tube pressure gauge might be +/- 1.6%. A digital gauge might be better or indeed worse on the data sheet as defined by a Technical Standard. Our take would be that the calibration certificate tells you what the actual accuracy is. We have had digital gauges where the calibration results are dramatically good.

Maybe the bigger question is whether a technician can read an old fashioned 63mm gauge to 1.6%. Then of course, does it matter? A 150mm test gauge might have a mirrored scale to cut parallax error but small gauges are quite tricky. With the best will in the world, a 63mm gauge is always going to have some error in reading it. A digital gauge is just digits that you read. Even a readout isn’t perfect if there is frantic activity on the display. That may only represent an utterly minute change. For day to day use, we are still massive fans of low tech traditional borden tube gauges for lots of applications. They carry on working and don’t need a battery. But then you can up your game incredibly by using a digital gauge.

So, the answer is that a digital gauge is very easy to read compared with a borden tube gauge and that alone might feed into “accuracy.” There are a few issues in this question.

What capabilities can a digital pressure gauge offer above an analogue gauge?

A Hydrotechnik data logging pressure gauge. Image courtesy Hydrotechnik.

Even basic digital pressure gauges are powerful. Our analogue gauges are dual scale, as would be any digital offering. Accuracy and the ability to read an accurate setting very quickly are big pluses. A digital unit can record a maximum pressure in a much more high-tech manner than a rudimentary (but serviceable) drag pointer borden tube gauge. Maybe the days are numbered for drag pointers, using a second point which is dragged round to a maximum position by the primary pointer. We would probably go digital every time now. Move on to recording pressure v time and most people would now go digital compared with a traditional chart recorder pressure gauge used for decades on process plant. That said, a paper chart recorder provides hard copy evidence in front of your eyes rather than a plot on a pc screen.

One other basic point on physically reading a gauge fitted to a Micropac pump or in a larger system. A technician needs to read an old fashioned borden tube gauge. Use a data logging digital gauge and the output moves to a laptop or mobile device via a cable or Bluetooth. You have then moved to remote monitoring of pressure. That is a big difference.

How expensive is it to recalibrate a digital and an analogue pressure gauge?

As any quality person will tell you, if a measuring instrument isn’t calibrated, it is only an indicator and of questionable value. If you are controlling a process or testing, you need the gauge slotted into a quality system, the calibration interval set and a calibration certificate. The certificate will be referenced back to a National Standard and maybe the more demanding UKAS standard. 

To recalibrate an analogue gauge, any calibration laboratory can probably certify it. They are comparing it to a master. The readings at certain points are recorded and if the error is within the BS or Din standard for the gauge, a certificate can be produced. Our experience would be that on our 63mm pressure gauges, if the instrument is out of specification, it will be discarded. Some gauges are undoubtedly adjustable. We might pay 25GBP to get a gauge recalibrated.

Move to digital pressure gauges and the same comparison to a master would be used. Again, you would hope that the gauge is within specification. Is there adjustment that can be made at the laboratory? We send our digital gauges back to the manufacturer, but can you send them back to any calibration laboratory? We don’t know the answer. We probably pay 50GBP, so more than analogue.

How important is a data logging output?

Hydrotechnik data logging software to process and display digital pressure gauge output. Image by Hydrotechnik.

The answer is very important indeed for instrumentation engineers and all the digital gauges we sell with our Micropac pumps offer this form output for use in presenting pressure readings. Pressure may just be one of numerous parameters that are being collected over time. A digital pressure gauge might just be capturing time and pressure as readings. If you can add in other parameters as well like multiple pressure points, temperature and displacements that might arise in monitoring whole systems. At Sarum Hydraulics, we would offer a digital pressure gauge with a data logger output. Engineers might have their own software, but Hydrotechnik can offer their software product. Read more on their product.

What format is the data logging output on our digital pressure gauge supplied with Micropac pressure test kit?

The standard output would be the .csv files stored on the gauge. Extract them using a cable to your device or using Bluetooth on a more advanced gauge. An instrumentation engineer would use these as files in a spreadsheet then corelate and construct the tables and templates themselves. The most common spreadsheet would be Excel. Alternatively, Hydrotechnik will provide excellent software to utilise and display these files.

Can I use the output from the Micropac MC-X pressure transducer directly into my pc?

Micropac MC-X miniature test pump with pressure transducer fitted.

There are two types of transducer we can offer.

On our Micropac PTR-A pressure cycling rig, we feed the output from the pressure transducer into a proprietary plc that controls the operation. We don’t get involved in integration of either the csv output from the data logger pressure gauge or transducer output into higher level instrumentation. Our only observation is that a proprietary plc is an amazing device for any industrial automation.  We don’t get involved with the programming of our own device or indeed any other applications using pressure transducers.

There are however, transducer models with a USB connection on the end, that plug straight into a PC, and send your time and pressure data directly into software for recording and visualising. You can then generate reports and certificates within the software. These models are popular for customers who wish to use the test data for proving results.

Why would I use a pressure transducer instead of a data logging digital pressure gauge?

Our understanding is that instrumentation people would run with the transducer to provide one of their measurements from a system.

Instrumentation engineers might use a pressure transducer instead of a datalogging pressure gauge when you need to capture very sudden pressure fluctuations or are feeding pressure into a real-time control system. The data logging solution might be more commonly found in a simple pressure testing application with just pressure and time as parameter. We do use transducers for more sophisticated applications, including our PTR-A programmable pressure cycling rig. This Mensor article provides background.

Conclusion on analogue versus digital pressure measurement.

This is an important question for hydraulics people. The world has moved on and recording maximum pressure or pressure v time on a system is most easily done using digital means. In our world there is still a place for traditional low cost borden tube pressure gauges rather than digital gauges on hydrostatic pressure test kit. Move to digital pressure gauges and pressure transducers to open up a world of processing pressure readings digitally for advanced testing.

Our starting point of “hydrostatic pressure testing” is quite a narrow application traditionally using a Borden tube pressure gauge. Using digital pressure gauges moves legacy hydrostatic testing on to recording and manipulating pressure data including over changes over time. Pressure transducers open this traditional equipment up to recording transients and pressure pulses.

This is our take after over 40 years of manufacturing our Micropac pressure test equipment. Buy a Micropac manual hydrostatic pressure test pump and order it with a data logging pressure gauge and you open up this world of digital pressure recording. Contact us with your question.

Micropac MW series on 2.5L fixed reservoir fitted with data logging digital pressure gauge and pressure transducer.