programmable voltmeter display - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: February 05, 2025, 09:20:07 pm
content: Manufacturers like truemeter make digital displays that will show the value and and analogue style meter readout of a voltage.But I need one that will show 2 voltages. I need to replace some ancient mechanical technology where a readout is shown and a trip point is set. I can easily do the logic with a comparator and a potentiometer for the input. I just need to be able to show the user the set point and the current value.

author: mikerj
author_rank: Super Contributor
timestamp: February 05, 2025, 10:06:13 pm
content: This is a kind of panel voltmeter HMI, you design how you want the display to look using their software and upload it. Two voltage inputs on this one.https://www.tester.co.uk/panelpilot-sgd-24-m-2-4-programmable-voltmeter-displayA larger (2.8") and slight more expensive version:https://www.tester.co.uk/panelpilot-sgd-28-m-2-8-programmable-voltmeter-display

author: pqass
author_rank: Super Contributor
timestamp: February 05, 2025, 10:24:31 pm
content: Yes it would be nice to see both set and actual values at the same time. Those Trumeter displays look good but they're expensive.But you could also just have a Set button to flip the output to the set value while pressed. Or the first turn/change of the set adjustment pot to flip the output to the set value. I do this with my DIY soldering station with just a 7-seg display and rotary encoder. It normally shows the actual temperature but if you just touch the encoder, it'll show the set value until you stop, then going back to actual value after 2 seconds.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 06, 2025, 06:01:40 am
content: Quote from: Simon on February 05, 2025, 09:20:07 pmHow many digits do you need ?Aliexpress have many modules that have dual displays. 3 and 4 digits and a quick scan shows 5 digits in single display, choice of 3 colours, so you could use two.The most common dual-use is for voltage and current, so you may need to modify the current by swap of the shunt for a voltage divider.

author: Simon
author_rank: Unknown
timestamp: February 06, 2025, 07:27:24 am
content: So what I am trying to replace is a hydraulic load cell. It has a gauge that shows the force and a needle that the user adjusts to set the limit. when this is reached a contact is made.So functionally this is a latched comparator, so I can do that with a comparator, but the actual visualization is the difficulty which is why what is essentially a mechanical user interface was used in the first place. They are no longer made so I am tasked with a one off replacement so there is no point in doing a full blown design. Couple of hundred pounds is just fine.

author: Poroit
author_rank: Frequent Contributor
timestamp: February 06, 2025, 09:13:58 am
content: G'day Simon,If I read this correctly, you would need install a pressure transmitter in the hydraulic circuit to get the electrical signal you need to operate a digital display.What is the range of the existing Force Gauge and what is the diameter of the Hydraulic Ram?P=F/A to determine the range of the pressure transmitter.

author: Simon
author_rank: Unknown
timestamp: February 06, 2025, 09:40:15 am
content: Well the existing unit is it's own little hydraulic circuit. It is literally a hydraulic/mechanical user interface with an electrical switch. You turn a knob, this sets a needle, the pressure needle pushes another stationary needle up so if the pressure get to the set needle thy make contact. the needle that "remembers" the last high pressure stays in place. The reading in transmitted hydraulically from the force sensor up to the gauge. This all means that without involving electronics they had a visual on the set point and the current reading.The machine itself does have a hydraulic circuit, so yes instead of finding an electrical load cell that will be quite expensive, we can use a pressure sensor instead in the hydraulics as the pressure does equate to the force. So 0-10V signal a potentiometer to compare to and it's fairly simple. The hard bit is the read out.Turns out we have a Unitronics HMI+PLC knocking about, yes expensive solution, but this is a one off repair and we already have it.

author: voltsandjolts
author_rank: Unknown
timestamp: February 06, 2025, 10:12:57 am
content: Would an off-the-shelf calibrated pressure sensor with programmable output trip point be helpful here?https://www.wika.com/en-gb/psd_4.WIKAAlso, remember to consider any safety issues early on to avoid nasty surprises. I mean, if the sensor fails for some reason, is there an overpressure relief to avoid potential safety issue.

author: Poroit
author_rank: Frequent Contributor
timestamp: February 07, 2025, 03:46:40 am
content: I have seen many of these Gauge/Switches before....used to sell/repair them.It is basically a pressure gauge with a Contact Module fitted.Do you have any pics of the Hydraulic setup and existing gauge?I would tackle it with a pressure transmitter (4-20mA output)and a Digital Indicating Indicator/Controller.Wika A10 is a good pressure product. Shinko JC Controller or similar.