Convert 0.5v-3v to 0-10v - Page 1
Forum section: electronics / projects

author: kolbep
author_rank: Frequent Contributor
timestamp: March 11, 2016, 07:49:08 pm
content: Here is my weekend project.I have a hih5030 humidity sensor that runs off 5v, and gives an output of 0.5v to 3v depending on rhthe instrument I need this to connect to, operates on the 0-10v rangethe instrument will connect to the converting board over about 15m of cat5 cable.what is the easiest way to upscale this? can I use transistors or is an opamp better?even if the output of my converter goes from say 1.5v (when sensor gives out 0.5v) up to 9v or something,I have some play on the controller instrument to set span and offsetthanks

author: Zero999
author_rank: Super Contributor
timestamp: March 11, 2016, 08:05:50 pm
content: See link below for a guide on how to design an op-amp circuit to do this.http://www.ti.com/lit/an/sloa097/sloa097.pdf

author: m98
author_rank: Frequent Contributor
timestamp: March 11, 2016, 08:17:12 pm
content: You should use a rail-to-rail op-amp, so you don't need to generate a negative supply rail.

author: Zero999
author_rank: Super Contributor
timestamp: March 11, 2016, 10:06:50 pm
content: It doesn't need to be rail-to-rail, unless the power supply voltage is under 12V. A single power supply op-amp such as the LM358 will do.

author: uncle_bob
author_rank: Unknown
timestamp: March 12, 2016, 01:47:00 am
content: Quote from: kolbep on March 11, 2016, 07:49:08 pmHiWhat is the accuracy of your sensor?What is the accuracy of your instrument?The sensor runs over 1/3 the range of your instrument. If the sensor is a 10% gizmo (pretty good for RH) and the instrument is a 0.1% gizmo (a 10 bit converter, not so great), there is no need to do anything at all.Bob

author: kolbep
author_rank: Frequent Contributor
timestamp: March 12, 2016, 06:18:40 am
content: The HIH5030 has an accuracy of +-3%And it's Output Voltage is calculated as : VOUT=(VSUPPLY)(0.00636(sensor RH) + 0.1515)I plan to use a 7805 regulator. So if we take the 2 extremes:Vout=5*(0.00636(0) + 0.1515) = 0.7575v (Zero Humidity)Vout=5*(0.00636(100)+0.1515) = 3.9375 (100 Humidity)The Icon Electronics Controller (P49-SM2-(10)-P) has the following specs:Specifications: Display offset: -999 to 9999Display span: -1999 to 9999Display resolution: 0.01 to 1.000 (adjustable)Input offset: 0 to 10.3V / 5.15VInput span: 0 to 10.3V / 5.15V (offset + span maximum = 10.3V)Measurement resolution: 10 mV Accuracy ±0.3% @ 25°C (% of full scale) Input voltage: ±15% of rated inputI am not looking for Super High Accuracy, It is for a Nut Kernel Drying Duct, so the Humidity would be set around 20 to 40 percent.We typically have the controller set to a 3% hysteresis anyway.So, Does this mean that I should be able to just connect the sensor to the controller,and set the offset, and span, and then should be fine?do you think there will be any problem with the HIH5030 driving the 15m line directly, or should I buffer it somehow?Quote

author: Zero999
author_rank: Super Contributor
timestamp: March 12, 2016, 02:36:54 pm
content: Quote from: kolbep on March 12, 2016, 06:18:40 amThe document I linked to shows you how to design a circuit to do that. Here it is again:http://www.ti.com/lit/an/sloa097/sloa097.pdf

author: uncle_bob
author_rank: Unknown
timestamp: March 12, 2016, 02:47:31 pm
content: Quote from: kolbep on March 12, 2016, 06:18:40 amHiThe only way you will know if the output needs buffering is to try in. An equally good question is if things need to be protected. The answers to both are pretty dependent on what else is running around in your system. If you have a few hundred KW being switched on and off to a dryer system that cables in a few cm away from the signal leads all along the 15 M run... the answer is yes to both the protection and buffering questions.From your description of the indicator / controller, it's already set up to handle the signal out of the humidity sensor just fine. I don't see any reason at all to mess with the signal for that part of it. You run the risk of messing things up and there is no real advantage to it.Best guess where you will end up:Pair of power leads going down to the sensorPair of signal leads coming back from the sensorPower goes to a full wave bridge (even if it's DC) and that feeds the 78L05.Regulator feeds the sensor and an op-amp wired as a gain of +1 followerOp amp output goes into a 100 ohm resistor to a pair of diodes and then to a 100 ohm resistor to the signal + wireGround on the regulator goes into a 200 ohm resistor to the signal - wireThe diodes on the resistor junction go: one to ground and the other to +5V.At the other end, your controller hooks to the two signal wires. Your floating power source hooks to the power leads.Bob

author: kolbep
author_rank: Frequent Contributor
timestamp: March 12, 2016, 08:14:08 pm
content: Thanks for all the help guys.I seem to have it figured out and working now (At Least on my Multimeter).The HIH Sensor operates from a local 7805 regulatorThe 12v Line (It is regulated) coming in from the control panel runs a local capacitor, the regulator and the opamp.I ran the HIH Sensor into an LM2904 Opamp with a gain of about 2.5Then on the output of the Opamp, I put 2 signal diodes in series to drop the offset that is caused by Amplifying the Sensors offset.Now if i really dry out the sensor, I almost get 0v out. Put it above a glass of steaming water, and I get 9.91v out. (So it looks like it handles 0-99% as 0-9.9v, which should be fine with me).As I said, I do not require too much accuracy (just a ball park)On Monday I will hook it up next to a commercial sensor in another dryer, and see if it corresponds, or if I need to play with the Span/Offset a bit.

author: Zero999
author_rank: Super Contributor
timestamp: March 12, 2016, 09:16:28 pm
content: Quote from: kolbep on March 12, 2016, 08:14:08 pmThat will be fine, as long as you can live with the temperature dependence of the diodes' forward voltage drop: try heating them with a soldering iron/hot air gun. If it's a problem then using the regulated 12V PSU to adjust the offset will be more accurate.

author: David_AVD
author_rank: Super Contributor
timestamp: March 12, 2016, 11:33:48 pm
content: Quote from: kolbep on March 12, 2016, 06:18:40 amIt would seem so. Try connecting via a short cable first to verify correct operation, then add the buffer if required.