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How can I make 20-200 ohm variable resistor look like a 20-240 ohm resistor?
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$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
(40R in series gives a full tank showing '3/4 full' on the dial: Still not ideal!).
resistance multiplier
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
|
show 1 more comment
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
(40R in series gives a full tank showing '3/4 full' on the dial: Still not ideal!).
resistance multiplier
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
2
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago
|
show 1 more comment
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
(40R in series gives a full tank showing '3/4 full' on the dial: Still not ideal!).
resistance multiplier
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
(40R in series gives a full tank showing '3/4 full' on the dial: Still not ideal!).
resistance multiplier
resistance multiplier
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
Stuart LeaskStuart Leask
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
Stuart LeaskStuart Leask
161
asked 8 hours ago
Stuart LeaskStuart Leask
161
161
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Stuart Leask is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
2
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago
|
show 1 more comment
$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
2
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago
$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
2
2
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago
|
show 1 more comment
3 Answers
3
active
oldest
votes
$begingroup$
I think the easiest way would be just getting a new variable resistor. You could use a transistor to switch in an extra resistance but potentiometers are pretty cheap, so swapping out would be the easiest option.
edited 8 hours ago
Greenonline
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
add a comment |
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
Status Spec. Actual Reading Voltage
------------------------------------------
Full 20 Ω 20 Ω 100% 160 mV
Empty 240 Ω 200 Ω 25% 1600 mV
Required voltage 1920 mV
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) What you've got. (b) The voltage reading can be boosted to the correct level by feeding an extra 1.6 mA through the sensor. (c) A simple current source based on 12 V supply and 1920 mV for empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
R4 looks simple to me.
I suspect that the 8 mA source is constant current so that the gauge doesn't fluctuate with revving of the engine (other than that gradual downward trend as you burn up the earth's carbon fuel reserves). To avoid R4 introducing variation you might want to feed it from a stable voltage source - as high as you reasonably can - and recalculate for your new voltage.
answered 5 hours ago
TransistorTransistor
92.1k788199
$endgroup$
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
add a comment |
$begingroup$
Per your comment "It's a digital gauge that runs about 8mA into the resistor in all positions", you don't actually need to make it "look like a resistor" from the gauge's point of view - you can just provide the gauge with a low-impedance voltage source, where that voltage is a linear function of the sensor resistance. A fairly straightforward op amp circuit should do the trick. You'll want to output a voltage that's 20*.008=0.16 V at one end of the scale and 240*.008=1.920 V at the other end of the scale.
answered 6 hours ago
pericynthionpericynthion
4,440929
$endgroup$
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
I think the easiest way would be just getting a new variable resistor. You could use a transistor to switch in an extra resistance but potentiometers are pretty cheap, so swapping out would be the easiest option.
edited 8 hours ago
Greenonline
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
add a comment |
$begingroup$
I think the easiest way would be just getting a new variable resistor. You could use a transistor to switch in an extra resistance but potentiometers are pretty cheap, so swapping out would be the easiest option.
edited 8 hours ago
Greenonline
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
add a comment |
$begingroup$
I think the easiest way would be just getting a new variable resistor. You could use a transistor to switch in an extra resistance but potentiometers are pretty cheap, so swapping out would be the easiest option.
edited 8 hours ago
Greenonline
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I think the easiest way would be just getting a new variable resistor. You could use a transistor to switch in an extra resistance but potentiometers are pretty cheap, so swapping out would be the easiest option.
edited 8 hours ago
Greenonline
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 8 hours ago
Greenonline
1,15331024
edited 8 hours ago
Greenonline
1,15331024
edited 8 hours ago
Greenonline
1,15331024
1,15331024
answered 8 hours ago
IgorLIgorL
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 8 hours ago
IgorLIgorL
492
answered 8 hours ago
IgorLIgorL
492
492
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
IgorL is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
add a comment |
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
indeed. its a gas gauge so you want some semblance of linearity and simple solutions will not provide that. that would require transistors to amplify and offset a voltage tuned by the pot and then used to drive a voltage controlled resistor.
$endgroup$
– DKNguyen
8 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
Since the potentiometer is an integral part of a fuel level sensor, it may not be practical either to find a suitable replacement or to get access to replace it.
$endgroup$
– pericynthion
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
@pericynthion However, the entire fuel level sensor may be a replaceable item.
$endgroup$
– TimWescott
6 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
$begingroup$
That's where this started - the original ran from 70-140 ohms, so I replaced with an unused item, that still is clearly some way off spec!
$endgroup$
– Stuart Leask
5 hours ago
add a comment |
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
Status Spec. Actual Reading Voltage
------------------------------------------
Full 20 Ω 20 Ω 100% 160 mV
Empty 240 Ω 200 Ω 25% 1600 mV
Required voltage 1920 mV
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) What you've got. (b) The voltage reading can be boosted to the correct level by feeding an extra 1.6 mA through the sensor. (c) A simple current source based on 12 V supply and 1920 mV for empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
R4 looks simple to me.
I suspect that the 8 mA source is constant current so that the gauge doesn't fluctuate with revving of the engine (other than that gradual downward trend as you burn up the earth's carbon fuel reserves). To avoid R4 introducing variation you might want to feed it from a stable voltage source - as high as you reasonably can - and recalculate for your new voltage.
answered 5 hours ago
TransistorTransistor
92.1k788199
$endgroup$
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
add a comment |
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
Status Spec. Actual Reading Voltage
------------------------------------------
Full 20 Ω 20 Ω 100% 160 mV
Empty 240 Ω 200 Ω 25% 1600 mV
Required voltage 1920 mV
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) What you've got. (b) The voltage reading can be boosted to the correct level by feeding an extra 1.6 mA through the sensor. (c) A simple current source based on 12 V supply and 1920 mV for empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
R4 looks simple to me.
I suspect that the 8 mA source is constant current so that the gauge doesn't fluctuate with revving of the engine (other than that gradual downward trend as you burn up the earth's carbon fuel reserves). To avoid R4 introducing variation you might want to feed it from a stable voltage source - as high as you reasonably can - and recalculate for your new voltage.
answered 5 hours ago
TransistorTransistor
92.1k788199
$endgroup$
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
add a comment |
$begingroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
Status Spec. Actual Reading Voltage
------------------------------------------
Full 20 Ω 20 Ω 100% 160 mV
Empty 240 Ω 200 Ω 25% 1600 mV
Required voltage 1920 mV
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) What you've got. (b) The voltage reading can be boosted to the correct level by feeding an extra 1.6 mA through the sensor. (c) A simple current source based on 12 V supply and 1920 mV for empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
R4 looks simple to me.
I suspect that the 8 mA source is constant current so that the gauge doesn't fluctuate with revving of the engine (other than that gradual downward trend as you burn up the earth's carbon fuel reserves). To avoid R4 introducing variation you might want to feed it from a stable voltage source - as high as you reasonably can - and recalculate for your new voltage.
answered 5 hours ago
TransistorTransistor
92.1k788199
$endgroup$
I have a fuel sender in my kit car that goes from 20R to earth (full) to 200R (empty). Unfortunately the gauge (constant current source, measuring resistance to earth?) expects empty to be 240 ohms, so displays '1/4 full' when empty.
Status Spec. Actual Reading Voltage
------------------------------------------
Full 20 Ω 20 Ω 100% 160 mV
Empty 240 Ω 200 Ω 25% 1600 mV
Required voltage 1920 mV
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) What you've got. (b) The voltage reading can be boosted to the correct level by feeding an extra 1.6 mA through the sensor. (c) A simple current source based on 12 V supply and 1920 mV for empty.
What is the simplest analogue way to make 20-200R look like 20-240R?
R4 looks simple to me.
I suspect that the 8 mA source is constant current so that the gauge doesn't fluctuate with revving of the engine (other than that gradual downward trend as you burn up the earth's carbon fuel reserves). To avoid R4 introducing variation you might want to feed it from a stable voltage source - as high as you reasonably can - and recalculate for your new voltage.
answered 5 hours ago
TransistorTransistor
92.1k788199
answered 5 hours ago
TransistorTransistor
92.1k788199
answered 5 hours ago
TransistorTransistor
92.1k788199
answered 5 hours ago
TransistorTransistor
92.1k788199
92.1k788199
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
add a comment |
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
$begingroup$
That looks just the ticket! I'll give it a whirl, thanks.
$endgroup$
– Stuart Leask
3 hours ago
add a comment |
$begingroup$
Per your comment "It's a digital gauge that runs about 8mA into the resistor in all positions", you don't actually need to make it "look like a resistor" from the gauge's point of view - you can just provide the gauge with a low-impedance voltage source, where that voltage is a linear function of the sensor resistance. A fairly straightforward op amp circuit should do the trick. You'll want to output a voltage that's 20*.008=0.16 V at one end of the scale and 240*.008=1.920 V at the other end of the scale.
answered 6 hours ago
pericynthionpericynthion
4,440929
$endgroup$
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
add a comment |
$begingroup$
Per your comment "It's a digital gauge that runs about 8mA into the resistor in all positions", you don't actually need to make it "look like a resistor" from the gauge's point of view - you can just provide the gauge with a low-impedance voltage source, where that voltage is a linear function of the sensor resistance. A fairly straightforward op amp circuit should do the trick. You'll want to output a voltage that's 20*.008=0.16 V at one end of the scale and 240*.008=1.920 V at the other end of the scale.
answered 6 hours ago
pericynthionpericynthion
4,440929
$endgroup$
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
add a comment |
$begingroup$
Per your comment "It's a digital gauge that runs about 8mA into the resistor in all positions", you don't actually need to make it "look like a resistor" from the gauge's point of view - you can just provide the gauge with a low-impedance voltage source, where that voltage is a linear function of the sensor resistance. A fairly straightforward op amp circuit should do the trick. You'll want to output a voltage that's 20*.008=0.16 V at one end of the scale and 240*.008=1.920 V at the other end of the scale.
answered 6 hours ago
pericynthionpericynthion
4,440929
$endgroup$
Per your comment "It's a digital gauge that runs about 8mA into the resistor in all positions", you don't actually need to make it "look like a resistor" from the gauge's point of view - you can just provide the gauge with a low-impedance voltage source, where that voltage is a linear function of the sensor resistance. A fairly straightforward op amp circuit should do the trick. You'll want to output a voltage that's 20*.008=0.16 V at one end of the scale and 240*.008=1.920 V at the other end of the scale.
answered 6 hours ago
pericynthionpericynthion
4,440929
answered 6 hours ago
pericynthionpericynthion
4,440929
answered 6 hours ago
pericynthionpericynthion
4,440929
answered 6 hours ago
pericynthionpericynthion
4,440929
4,440929
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
add a comment |
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
$begingroup$
Thanks - I was thinking of something around an op-amp, just wondered if there was something more elegant (related to a current mirror?) that anyone one of.
$endgroup$
– Stuart Leask
6 hours ago
add a comment |
Stuart Leask is a new contributor. Be nice, and check out our Code of Conduct.
Stuart Leask is a new contributor. Be nice, and check out our Code of Conduct.
Stuart Leask is a new contributor. Be nice, and check out our Code of Conduct.
Stuart Leask is a new contributor. Be nice, and check out our Code of Conduct.
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$begingroup$
If you want to modify what you have, you need to know the full details on the gauge.
$endgroup$
– Charles Cowie
8 hours ago
$begingroup$
Find a different gauge or a different sensor. Are they aftermarket units? Can they be reworked?
$endgroup$
– TimWescott
8 hours ago
$begingroup$
When you hook a 240$Omega$ resistor to the gauge, what's the voltage (or, alternately, what's the current?)
$endgroup$
– TimWescott
8 hours ago
$begingroup$
Can you change the location of the markings on the gauge?
$endgroup$
– Andrew Morton
8 hours ago
2
$begingroup$
It may be the best you can do easily without changing the gauge. Empty is the important point on the dial anyway.
$endgroup$
– Spehro Pefhany
8 hours ago