Hobbyist grade calibrator able to automate signal sourcing and measurements - Page 1
Forum section: electronics / testgear

author: krzychb
author_rank: Contributor
timestamp: February 11, 2018, 11:51:31 am
content: Hello everybody,I am looking for a help finding a calibrator that can be controlled remotely by e.g. a serial to automate calibration process. It should be within a price range for a hobbyist. A good example would be MR9270S that allows setting of mV or mA source and taking measurement by RS485 modbus.A short description with links is underhttps://isojed.nl/blog/2016/12/24/mr-signal/,.Below is an example of remote control:.My concern with MR9270S is that I can not find any working webpage of the producer. Do you know if this device is still produced and firmware updates are avialable?If not, what other similar calibrators could you recommend?

author: amspire
author_rank: Super Contributor
timestamp: February 11, 2018, 01:41:50 pm
content: What do you want to calibrate?I am also not sure why a hobbyist needs an automated calibration.

author: JDubU
author_rank: Frequent Contributor
timestamp: February 11, 2018, 01:44:37 pm
content: Is this what you are looking for?http://www.lanyigs.com/en/

author: Kean
author_rank: Unknown
timestamp: February 11, 2018, 02:02:02 pm
content: Seems to be cheaper on Banggoodhttps://www.banggood.com/MR9270S-4-20mA-Signal-Generator-Calibration-Current-Voltage-PT100-Thermocouple-Pressure-Transmitter-p-1103449.htmlReviews there are generally quite positive

author: krzychb
author_rank: Contributor
timestamp: February 11, 2018, 02:32:35 pm
content: Quote from: amspire on February 11, 2018, 01:41:50 pmI would like to characterize an internal amplifier of a batch of 10 - 20 chips and then, depending on results, maybe repeat it for another batch. I would like to automate the process of setting the input voltage and taking the readings. Having the functionality like MR9270S provides I should be able to do it with a simple script.Quote from: JDubU on February 11, 2018, 01:44:37 pmYes, that's the site. It does not respond and I see other people saying so.

author: amspire
author_rank: Super Contributor
timestamp: February 11, 2018, 11:31:07 pm
content: Quote from: krzychb on February 11, 2018, 02:32:35 pmAn application like that is well within the bounds of an Arduino-type circuit with a few extra parts. PWM plus a good reference voltage can easily generate programmable voltages to much better then 0.1% accuracy, and you can get Arduino chips with 12 bit A/D such as the $2 STM32 based boards with 2 x 12 bit A/D converters and 10 input analog channels:https://www.aliexpress.com/item/STM32F103C8T6-ARM-STM32-Minimum-System-Development-Board-Module-For-Arduino-Micro-USB-controller-ARM-Learning-Board/32841974737.htmlI do understand the convenience of ready-to-run gear. Just be aware that when they quote 0.05% accuracy for the DC out on the MR9270S, that may be only at 12V out. Companies like Fluke are very precise and conservative in their specs. Fluke may be using custom divider networks to ensure long term stability, whereas cheap calibrators may be relying on off-the-shelf metal film resistors that can drift. Cheaper devices tend to have vaguely worded specs that are not conservative.For the 12V out, the MR9270S is quoting an internal impedance of 500K ohms which is very high. It could be an unbuffered PWM output or it may be they added a big series resistor to the output to make it indestructable. If their own specs are correct, it is almost unusable without an additional precision voltage follower to buffer the output.According to their own specs, if the 12V out is connected to the input, it should read 6V.The 100 ohm internal impedance for the current outputs does not make sense as current sources need impedances well into the high megohms. Again, I assume this means the source has a series 100 ohm series resistor for protection.

author: JDubU
author_rank: Frequent Contributor
timestamp: February 12, 2018, 12:58:58 am
content: Quote from: krzychb on February 11, 2018, 02:32:35 pmIt works for me. Here is the link to their Manual, firmware, and software download location on Google Drive:https://drive.google.com/drive/folders/0B6iPRCTgiPZjazhDT1RJYW9sUjA

author: krzychb
author_rank: Contributor
timestamp: February 12, 2018, 05:29:46 am
content: Quote from: JDubU on February 12, 2018, 12:58:58 amThanks @JDubU!I already suspected the producer "lanyigs" does not exist anymore.For some reason the websitehttp://www.lanyigs.com/time outs for me.

author: krzychb
author_rank: Contributor
timestamp: February 12, 2018, 11:21:46 am
content: Quote from: amspire on February 11, 2018, 11:31:07 pmThank you for suggestions, review of the MR9270S specs and pointing out potential pitfalls.They are all good points and made me think over my approach.

author: sotos
author_rank: Frequent Contributor
timestamp: February 12, 2018, 11:27:11 am
content: Because I am also interested for this item, please tell us your final thought.

author: krzychb
author_rank: Contributor
timestamp: February 13, 2018, 10:04:03 am
content: Quote from: sotos on February 12, 2018, 11:27:11 amFor the price I like the range of functions offered, especially ability to control calibrator remotely with Modbus and good documentation. I am discouraged with the impedance of the voltage source as pointed out by @amspire, ref. page 3 ofdocumentation.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: February 13, 2018, 10:56:10 am
content: My assumption is that they might have just mixed up the voltage and current output impedance when giving those specs. A voltage source with an output impedance of 500k is going to give you very large errors except when you are measuring with something like a high-end bench meter with several gigaohm input impedance. Into a 10 Mohm handheld meter it'll already have a few percent error due to loading.

author: amspire
author_rank: Super Contributor
timestamp: February 13, 2018, 11:07:25 am
content: Quote from: TheUnnamedNewbie on February 13, 2018, 10:56:10 amThat is probably true, but if the person who wrote the specifications didn't understand what he/she was talking about, how can you believe anything in the specifications?