diff --git a/.idea/inspectionProfiles/Project_Default.xml b/.idea/inspectionProfiles/Project_Default.xml
index 1d0929c..0689107 100644
--- a/.idea/inspectionProfiles/Project_Default.xml
+++ b/.idea/inspectionProfiles/Project_Default.xml
@@ -33,5 +33,6 @@
         </list>
       </option>
     </inspection_tool>
+    <inspection_tool class="YAMLIncompatibleTypes" enabled="false" level="WARNING" enabled_by_default="false" />
   </profile>
 </component>
\ No newline at end of file
diff --git a/README.md b/README.md
index a6a158a..46e700c 100644
--- a/README.md
+++ b/README.md
@@ -41,7 +41,10 @@ to any number of different targets, such as databases or MQTT.
 * Supports arbitrary _**grouping of devices**_
   * A group can be for example "Heating" or "Lights". This allows users to get a better overview of their energy 
     consumption when many circuits and devices are involved.
-* Can apply various _**filters**_ to the power sensor data (clamping, high-pass etc.)
+* Can apply various _**filters**_ to the power sensor data, such as:
+  * Clamp values, useful for ignoring negative readings from bi-directional sensors
+  * High-pass filtering, useful for ignoring tiny power readings
+  * Scaling, often essential when dealing with Modbus sensors
 * Can _**measure unmetered power**_ too
   * You can have a current-transformer type sensor measuring a circuit, then a smart plug measuring some specific 
     device on that circuit, then an unmetered type sensor which calculates the difference between the two, yielding the 
diff --git a/package-lock.json b/package-lock.json
index a004a03..141233e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
       "license": "GPL-3.0-or-later",
       "dependencies": {
         "@influxdata/influxdb-client": "^1.33.2",
+        "async-mutex": "^0.5.0",
         "modbus-serial": "^8.0.16",
         "mqtt": "^5.1.2",
         "set-interval-async": "^3.0.3",
@@ -2094,6 +2095,15 @@
       "resolved": "https://registry.npmjs.org/async/-/async-3.2.4.tgz",
       "integrity": "sha512-iAB+JbDEGXhyIUavoDl9WP/Jj106Kz9DEn1DPgYw5ruDn0e3Wgi3sKFm55sASdGBNOQB8F59d9qQ7deqrHA8wQ=="
     },
+    "node_modules/async-mutex": {
+      "version": "0.5.0",
+      "resolved": "https://registry.npmjs.org/async-mutex/-/async-mutex-0.5.0.tgz",
+      "integrity": "sha512-1A94B18jkJ3DYq284ohPxoXbfTA5HsQ7/Mf4DEhcyLx3Bz27Rh59iScbB6EPiP+B+joue6YCxcMXSbFC1tZKwA==",
+      "license": "MIT",
+      "dependencies": {
+        "tslib": "^2.4.0"
+      }
+    },
     "node_modules/babel-jest": {
       "version": "29.7.0",
       "resolved": "https://registry.npmjs.org/babel-jest/-/babel-jest-29.7.0.tgz",
@@ -5613,6 +5623,12 @@
       "optional": true,
       "peer": true
     },
+    "node_modules/tslib": {
+      "version": "2.7.0",
+      "resolved": "https://registry.npmjs.org/tslib/-/tslib-2.7.0.tgz",
+      "integrity": "sha512-gLXCKdN1/j47AiHiOkJN69hJmcbGTHI0ImLmbYLHykhgeN0jVGola9yVjFgzCUklsZQMW55o+dW7IXv3RCXDzA==",
+      "license": "0BSD"
+    },
     "node_modules/type-check": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.4.0.tgz",
diff --git a/package.json b/package.json
index e1ec2f2..cca457c 100644
--- a/package.json
+++ b/package.json
@@ -32,6 +32,7 @@
   },
   "dependencies": {
     "@influxdata/influxdb-client": "^1.33.2",
+    "async-mutex": "^0.5.0",
     "modbus-serial": "^8.0.16",
     "mqtt": "^5.1.2",
     "set-interval-async": "^3.0.3",
diff --git a/src/circuit.ts b/src/circuit.ts
index 907063e..657eef9 100644
--- a/src/circuit.ts
+++ b/src/circuit.ts
@@ -1,4 +1,5 @@
 import { PowerSensor, PowerSensorData } from './sensor'
+import { applyFilters } from './filter/filter'
 
 export enum CircuitType {
   Main = 'main',
@@ -28,10 +29,24 @@ export const pollPowerSensors = async (
   const promises = []
 
   for (const circuit of circuits) {
-    const sensor = circuit.sensor
-
-    promises.push(sensor.pollFunc(timestamp, circuit, existingSensorData))
+    promises.push(pollPowerSensor(timestamp, circuit, existingSensorData))
   }
 
   return Promise.all(promises)
 }
+
+const pollPowerSensor = async (
+  timestamp: number,
+  circuit: Circuit,
+  existingSensorData?: PowerSensorData[],
+): Promise<PowerSensorData> => {
+  const sensor = circuit.sensor
+
+  let data = await sensor.pollFunc(timestamp, circuit, existingSensorData)
+
+  if (sensor.filters) {
+    data = applyFilters(sensor.filters, data)
+  }
+
+  return data
+}
diff --git a/src/eachwatt.ts b/src/eachwatt.ts
index 4872454..1f813b7 100644
--- a/src/eachwatt.ts
+++ b/src/eachwatt.ts
@@ -11,7 +11,6 @@ import { pollCharacteristicsSensors } from './characteristics'
 import { createLogger, LogLevel, setLogLevel } from './logger'
 import { setRequestTimeout as setHttpRequestTimeout } from './http/client'
 import { setRequestTimeout as setModbusRequestTimeout } from './modbus/client'
-import { applyFilters } from './filter/filter'
 import { setIntervalAsync } from 'set-interval-async'
 
 // Set up a signal handler, so we can exit on Ctrl + C when run from Docker
@@ -65,11 +64,6 @@ const mainPollerFunc = async (config: Config) => {
 
   // Post-process power sensor data
   powerSensorData = powerSensorData.map((data) => {
-    // Apply optional data filters
-    if (data.circuit.sensor.filters) {
-      data = applyFilters(data.circuit.sensor.filters, data)
-    }
-
     if (data.power !== undefined) {
       // Round all numbers to one decimal point
       data.power = Number(data.power.toFixed(1))
diff --git a/src/filter/filter.ts b/src/filter/filter.ts
index 1f1cb64..a7ecf1e 100644
--- a/src/filter/filter.ts
+++ b/src/filter/filter.ts
@@ -3,6 +3,7 @@ import { PowerSensorData } from '../sensor'
 export type PowerSensorFilters = {
   clamp?: 'positive'
   highPass?: number
+  scale?: number
 }
 
 export const applyFilters = (filters: PowerSensorFilters, data: PowerSensorData): PowerSensorData => {
@@ -21,5 +22,11 @@ export const applyFilters = (filters: PowerSensorFilters, data: PowerSensorData)
     data.power = 0
   }
 
+  // Scale
+  const scale = filters?.scale
+  if (scale !== undefined) {
+    data.power = data.power / scale
+  }
+
   return data
 }
diff --git a/src/modbus/client.ts b/src/modbus/client.ts
index fda7106..8ee9fc7 100644
--- a/src/modbus/client.ts
+++ b/src/modbus/client.ts
@@ -11,14 +11,16 @@ export const setRequestTimeout = (timeoutMs: number) => {
   logger.info(`Using ${timeoutMs} millisecond timeout for Modbus operations`)
 }
 
-// Keep track of clients, use one per address
+// Keep track of clients, use one per address/port/unit combination
 const clients = new Map<string, ModbusRTU>()
 
-export const getClient = (address: string): ModbusRTU => {
-  if (!clients.has(address)) {
+export const getClient = (address: string, port: number, unit: number): ModbusRTU => {
+  const key = `${address}_${port}_${unit}`
+
+  if (!clients.has(key)) {
     const client = new ModbusRTU()
-    clients.set(address, client)
+    clients.set(key, client)
   }
 
-  return clients.get(address) as ModbusRTU
+  return clients.get(key) as ModbusRTU
 }
diff --git a/src/sensor/modbus.ts b/src/sensor/modbus.ts
index 2c53694..31db6d5 100644
--- a/src/sensor/modbus.ts
+++ b/src/sensor/modbus.ts
@@ -5,11 +5,13 @@ import { createLogger } from '../logger'
 import { getClient, requestTimeout } from '../modbus/client'
 import { getRegisterLength, ModbusRegister, RegisterType, stringify } from '../modbus/register'
 import ModbusRTU from 'modbus-serial'
+import { Mutex } from 'async-mutex'
 
 export const DEFAULT_PORT = 502
 export const DEFAULT_UNIT = 1
 
 const logger = createLogger('sensor.modbus')
+const mutex = new Mutex()
 
 export const getSensorData: PowerSensorPollFunction = async (
   timestamp: number,
@@ -18,10 +20,10 @@ export const getSensorData: PowerSensorPollFunction = async (
   const sensor = circuit.sensor as ModbusSensor
   const sensorSettings = sensor.modbus
 
-  const client = getClient(sensorSettings.address)
+  const client = getClient(sensorSettings.address, sensorSettings.port, sensorSettings.unit)
 
   try {
-    // Connect if not connected yet
+    // Connect if not connected yet, skip
     if (!client.isOpen) {
       logger.info(`Connecting to ${sensorSettings.address}:${sensorSettings.port}...`)
       await client.connectTCP(sensorSettings.address, {
@@ -32,6 +34,14 @@ export const getSensorData: PowerSensorPollFunction = async (
       client.setID(sensorSettings.unit)
       // Request timeout
       client.setTimeout(requestTimeout)
+
+      // Wait 100 ms for the port to open, if it's not open, give up and return empty data
+      await new Promise((resolve) => setTimeout(resolve, 100))
+
+      if (!client.isOpen) {
+        logger.warn(`Modbus TCP channel not open after 100ms, will not attempt to read values this tick`)
+        return emptySensorData(timestamp, circuit)
+      }
     }
 
     // Read the register and parse it accordingly
@@ -58,16 +68,19 @@ const readRegisters = async (
   const address = register.address
   const length = getRegisterLength(register)
 
-  switch (register.registerType) {
-    case RegisterType.HOLDING_REGISTER:
-      return client.readHoldingRegisters(address, length)
-    case RegisterType.INPUT_REGISTER:
-      return client.readInputRegisters(address, length)
-    case RegisterType.COIL:
-      return client.readCoils(address, length)
-    case RegisterType.DISCRETE_INPUT:
-      return client.readDiscreteInputs(address, length)
-  }
+  // Serialize access to the underlying Modbus client
+  return mutex.runExclusive(async () => {
+    switch (register.registerType) {
+      case RegisterType.HOLDING_REGISTER:
+        return client.readHoldingRegisters(address, length)
+      case RegisterType.INPUT_REGISTER:
+        return client.readInputRegisters(address, length)
+      case RegisterType.COIL:
+        return client.readCoils(address, length)
+      case RegisterType.DISCRETE_INPUT:
+        return client.readDiscreteInputs(address, length)
+    }
+  })
 }
 
 const parseReadRegisterResult = (result: ReadRegisterResult | ReadCoilResult, register: ModbusRegister): number => {
diff --git a/tests/filter/filter.test.ts b/tests/filter/filter.test.ts
index 2db1735..405656c 100644
--- a/tests/filter/filter.test.ts
+++ b/tests/filter/filter.test.ts
@@ -2,7 +2,6 @@ import { emptySensorData, PowerSensorData, SensorType } from '../../src/sensor'
 import { applyFilters, PowerSensorFilters } from '../../src/filter/filter'
 import { Circuit } from '../../src/circuit'
 import { getSensorData as getDummySensorData } from '../../src/sensor/dummy'
-import exp = require('node:constants')
 
 test('clamping works', () => {
   const filters: PowerSensorFilters = {}
@@ -21,7 +20,7 @@ test('clamping works', () => {
   expect(data.power).toEqual(0)
 })
 
-test('high-pas works', () => {
+test('high-pass works', () => {
   const filters: PowerSensorFilters = {}
   let data: PowerSensorData = dummySensorData()
 
@@ -38,6 +37,20 @@ test('high-pas works', () => {
   expect(data.power).toEqual(3)
 })
 
+test('scale works', () => {
+  const filters: PowerSensorFilters = {}
+  let data: PowerSensorData = dummySensorData()
+
+  data.power = 155
+  data = applyFilters(filters, data)
+  expect(data.power).toEqual(155)
+
+  data.power = 155
+  filters.scale = 0.1
+  data = applyFilters(filters, data)
+  expect(data.power).toEqual(1550)
+})
+
 const dummySensorData = (): PowerSensorData => {
   const circuit: Circuit = {
     name: 'dummy',