Question about 4 Decade Resistance Box - Page 1
Forum section: electronics / testgear

author: toddc72
author_rank: Newbie
timestamp: October 15, 2024, 06:57:41 am
content: Newbie here. I have a question on this or these in general:https://www.hbarsci.com/products/ph1133pln10I took electronics in high school a long time ago and like it but only tinker in this stuff. Here is reason asking question on this. I have a PRI Sensor Simulator. Here is a pic of it from net.https://storeys.hibid.com/lot/35936155/pri---sst-iii-sensor-simulator-tester-for-obd.I have a box of gauges and senders mixed together. The simulator i have will only go down to 80 ohms minimum. You dial in the output you want and hit trigger and it outputs. I would like to go lower. Like 0 to 80 ohm range to cover this area since i seen some gauges use 0 to 30 ohms for readings. If I hook up the Decade Resistance Box to my gauge I am testing. With the positive and negative powering the gauge. Would this box than give me the output signal I am looking for to the gauge to read. This way I can mark on gauge what ohm sender is needed to work with it. I use the simulator now I currently have and mark on the gauges it works with of 80 to 230 ohms range.ThanksToddLiking the site. Lots of info here. Looks like going to be staying up late for awhile now reading the posts.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 15, 2024, 07:49:07 am
content: Yes, it'll work, but you should probably keep an eye on how much power is flowing through the decade resistor; measure the volts drop across it with a high impedance DMM (10MΩ should be good enough), and make sure you don't exceed the 2W power rating (using Ohm's Law).

author: toddc72
author_rank: Newbie
timestamp: October 15, 2024, 08:20:01 am
content: Thanks for replay. It is for automobile gauges. Like fuel level and oil pressure. So 12 volt dc is what I am using for the gauges but will still take into consideration about ohms law. Typical setup would be. A sender having output signal and also being grounded to housing. This I could read with a volt/ohm meter. Than the gauge has signal, ( + ) and ( - ). So figure if like my current signal generator is. I would hook up the ( + ) and the ( - ) power. Than run ( - ) through Decade box into input signal on gauge and adjust the value on box to see what sender is used with it. Unless there is a better way to do it? Seems in theory it should work. Just not 100 percent sure before I order one. Just seems like it should work as a variable sender would.Thanks again

author: tggzzz
author_rank: Super Contributor
timestamp: October 15, 2024, 10:40:20 am
content: As AVR points out, the traditional failure mode with decade resistance boxes is that the lowest value resistor(s) get toasted.If, like me, you don't trust yourself not to make a mistake, then you might like to take precautions.Determine the max allowable current through the low-value resistors. That should be written on the decade box.For your power supply, determine the resistor that would allow that current to flow; simple R=V/I.Insert that value of resistance in series with the decade box; even if the decade box is set to minimum ohms, it will not be damaged. Of course the combination of the decade box's max current R might be too high for your tests. In that case you will have to get a higher power decade box, reduce V, or be careful and hope you don't slip up